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.
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.
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.