In ancient times -- you know, the 1970s and '80s -- bicycle technology was mostly simple and accessible. Beginning with Shimano's introduction of Rapidfire in 1990, the industry has been systematically destroying that, but you can still find it.
Someone who has evolved with the bicycle over the past several decades will understand what the new stuff is trying to do, based on its ancestors. The processes are simple. The new crap just uses more complex internal parts to achieve the same basic objectives.
Most sophisticated modern componentry can't be repaired. And why would you? The stuff you bought this year has already been thrown on the scrap heap by the manufacturer. And yet, people persist in keeping their bike equipment for as long as they can, and trying to get it fixed when it malfunctions.
There are plenty of YouTube videos of people fixing things. Personally, I would rather have an exploded diagram and a brief, written synopsis of what's inside something than watch someone who may or may not know what they're doing demonstrate it in a video, but I'm old, cantankerous, and independent. But I digress...
Through the efforts of intrepid people doing what they've been told they can't, the independent mechanic community has discovered some of the inner mysteries of modern widgets that have accidentally been made accessible enough to open up, explore, and attempt to repair. Sometimes the repair depends on having donor organs available from another specimen that may conveniently have failed in a different way. Other times, the inner mysteries just need a good cleaning.
When bikes were truly simple and accessible, a rider could perform complete disassembly and reassembly in a small room with simple tools. Some of them had to be bike-specific, but they would all fit into a small toolbox. You could fake a work stand and a truing stand in various ways, although those items do make even simple maintenance luxuriously easier. When I was briefly well funded in the late 1990s, I bought shop-quality versions of both of those. But without them I still managed to build wheels and perform complete overhaul after complete overhaul through the years.
I don't say you need to be so ambitious. I only point out that it was possible. My riding buddies and I did invest in a truing stand that we owned communally and passed around so that we could each build wheels for our commuting and racing bikes. It was a beat-up old thing, not a real shiny Park, but it got us started. Other than that, we got by with improvised facilities wherever we lived. Our apartments always had telltale handlebar scuffs on the walls of the sparsely-furnished living room. In one apartment, my crazy friend Mark painted the rear stays of his racing bike fluorescent orange, leaving the outline on the wall. It was a pretty slummy apartment. I'm not sure whether we even lost our security deposit over that. The owner of the building may have thought she owed us some compensation for the cockroaches and the lack of heat.
Fast forward to the present day: I was digging around inside a SRAM Rival brifter that had suddenly stopped responding to commands. SRAM lets you right in there. I've even seen at least one video in which the rogue mechanic shows how easy they are to service. "Easier than Campy," he says. Even now, we still relate high end road stuff to Campagnolo. The thing is, Campagnolo provides parts and service instructions, or at least they did a couple of cogs ago. In the past several seasons, I have not had to delve into anything later than very early 10-speed from the Italians, if anything. I have not bothered to keep up, because I need brain space for more common issues.
SRAM does provide ample access to the interior of their brifters. After that, you're on your own. Since the simple task of changing a shift cable can involve removing the handlebar tape and exercising a large portion of your profanity supply, anything deeper than that will take a lot of time and require that you keep track of a lot of little parts. And therein lies the economic problem.
A shop has overhead. Back in the 1990s, mechanics learned as quickly as they could to fix as many esoteric problems as possible, because an active riding population was constantly challenging us to prove that we knew our stuff. The industry steadily added complexity and buried the mysteries under more layers of concealment, but the changes were incremental enough, and the equipment remained mostly simple enough for a good wrench to maintain some level of stature from season to season. And it made financial sense for the shop to project this image of expertise. Riders would tell their friends where to get the good work. They might buy bikes by price and brand image, but enough people were really riding to understand the value of reliable repairs.
As complexity reached ridiculous levels and the industry had simultaneously managed to wedge rider groups firmly apart, all-around expertise became harder to maintain. Riders, particularly in hard-core mountain and road categories, now want to go where they recognize the nonverbal signs of group allegiance. The divisions were always there. Now they are more starkly prominent. But, beneath it all, certain mechanical concepts still make everything work. So a shop that may not appear obviously in with the in-crowd may still have a person or two on the staff who can get into a mechanism, figure out what ails it, and fix it or definitively declare it dead.
Unlike the hospital, our shop tends not to charge the customer if the patient dies. This means that we have to make our assessment quickly enough that we haven't lost a lot of billable hours. And, if we think it might be repairable by someone more in tune with a particular bike type, we say so. In the case of the SRAM brifter, we ordered and installed a new one. Then I started an autopsy on the old one. The ratchets are not engaging correctly, and probably cannot be stabilized. Donor parts from another unit might work, but the experiment would take hours, at shop rates.
It makes no sense for the customer to invest in that or the shop to spend the time. But a bike owner with mechanical aptitude and spare time might get in there, diagnose the problem, scrounge up the parts, fix the unit, and announce triumphantly that shops are ripping you off when they say your brifter has to be replaced. Total cost in commercial shop hours might have been $300 for a part that retails new for $114, but that part of the calculation is ignored.
What the industry deems unfixable they will make sure really is unfixable. Until some mad scientist develops a little machine for home mechanics to clone repair parts using recycled plastic bottles and metal cans, powered by scampering cockroaches or little solar panels, true repairs will be the exception.