Even if assembly doesn't directly make a lot of profit, it's a great time to sell accessories and service plans.
Yes but then you miss out on an almost "bonding" experience with the machine and feeling of intimately understanding it. That's why I do most of my own car repair, even though it takes me longer than a shop would take.
Read Zen and the Art of Motorcycle Maintenance about the "Romantic" vs. "Classical" approach to such things.
That's true. Thirty years ago I had more time than money and working on my stuff was very satisfying. These days I would rather go to the movies with my wife, help my kids with their homework, walk my dog, or take a nap. I'm doing better financially, but my time is scarce.
I've read Zen. I loved the motorcycle travelogue part and but was bored by his treatise on quality.
Derailleurs are easy once you know how to set the limit screws and adjust the cable tension. Disc brakes are tricky, but again if you know the trick then it's pretty easy as well.
Then the derailleur spring will bring the chain all the way to the highest gear (smallest cassette cog), and since you backed the limit screw out, the chain will want to rub against the frame stays.
Use your fingers to push the derailleur up into a lower gear and then turn the limit screw for the outside limit one full turn. Repeat this until without using your hand to guide the derailleur the chain rests in the highest gear without needing any force, but also doesn't rub against the frame stay.
Then use your hand to push the derailleur all the way to the lowest gear (largest cassette cog) and try to get the chain to fall between the cassette and the wheel spokes. If it can fall over the inside of the gear and into the spokes then turn the limit screw for the inside limit one full turn. Repeat until the chain can reach the lowest gear without using excessive force, but cannot fall off the cog toward the spokes.
Add some lock tight to both limit screws so that you don't have to adjust them again, and you are done!
Now just reattach the rear derailleur cable and adjust the tension if you need to.
Naturally, it can take time to get parts, so if something is actually broken, then the bike is out of commission for a while. But a minor benefit of poor urban planning is that I've got space for a spare bike or two, or three, plus a bucket of spares that I've collected over the years from trashed bikes. ;-)
Also, doing the work at home means that there's less of an impediment to keeping the bike in good adjustment more or less continually, so parts don't come loose and start to deteriorate. Major repairs become less frequent. More or less weekly, I go down into the garage and check all of the bikes in the family fleet. The effort is practically trivial. I also involve the kids in this work, whenever possible.
With an eye towards doing my own maintenance, I choose my battles when I get a new (or more likely, used) bike. I prefer parts that are likely to be reliable, and that are straightforward to adjust without a proliferation of special tools.
Fortunately, they're also boneheadedly simple machines to fix. You can learn to change an inner tube, align a derailleur, adjust a brake caliper and true a wheel in about an hour. If you have those skills, you can do 90% of your own repairs. You'll have an infinitely better cycling experience, because you won't end up stranded at the side of the road because of something that could be fixed in two minutes.
I've spent months, maybe years, of time fixing and maintaining cars, motorcycles, and bicycles. It's useful when something breaks on the side of the road or when you get an estimate for repair. There is the satisfaction of being self-sufficient and able to do it yourself. There's also the screaming frustration when you break something-- which happens when you're learning like over-torquing a bolt (tighten until it spins then back off a quarter, anyone?). cracking a housing, snapping the head off a stuck bolt, watching a unique and critical part improbably pick up speed on a flat work area as it rolls away from you drawn to the siren song of a sewer grate or a gap in the deck. I want to spend time with family, friends, on hobbies, or, you know, actually use my vehicle instead of recreationally bust my knuckles on it. I'm happy to read all the manuals and squint at exploded diagrams then pay someone else to do it while I go play.
The other model I've seen work locally is demoing high end bikes. Specifically mountain bikes. The local shop has a weekly mountain bike ride where you can try out several bikes. This is probably worth the effort if they sell a couple extra bikes a week. The mountain bikes they demo range from $3-6k. This shop has bikes on the show floor, but could easily switch to demo only.