Bikes are much easier to maintain than they have been in the past. Mechanical 1x drive trains are much easier to fine tune than anything with a front derailleur. I'll take cable actuated disk brakes over cantilever brakes any day of the year. Outboard bearing bottom brackets are much simpler than square tapered bottom brackets - I never want to see a crank puller ever again in my life. Threaded stems always felt like a kludge.

Many more specialized parts of bikes: suspension (especially rear), tubeless tires, electronic shifting are optional. If you spend $10,000+ on a bike, there may be some parts that are more persnickety than others to a garage wrench turner.

The one good tool to get to make things go much more smoother is an accurate torque wrench for things like bottom bracket installation. If you've got fancy carbon parts (which I do not), you need another, smaller one for smaller nm of torque(s).

Also, what are we comparing bike to? They're easier than a motorcycle, and much of a motorcycle is easy enough to work on at home if you have the curiosity. What modern bike parts are (which I'll concede) in many cases are more delicate. I don't like how thin my 11spd chain is compared to the 9spd I started out with, and I don't like how sensitive to wear the entire drivetrain is either, but thems the breaks. Proper cleaning and lubing is just that much more important.