Common sense isn't so common. Basic mechanical knowledge isn't an emphasis of skills/experience being passed down in many families, especially those that have the financial resources to buy late model vehicles and have them worked on in shops. I'm guilty of this with my own kids. I grew up a lot less well off than I am now, and the things that I had to do to my junker cars - small repairs, oil changes, tire changes, tuneups, etc. - just aren't necessary or aren't possible/desirable (HOA with prohibitions on work on cars in driveways) with the vehicles I currently own. For better or worse, my focus on home-based learn-by-doing has been geared towards my own professional livelihood skills (passing on my trade) and only skimmed what used to be basic life skills (keeping a car on the road) that I am now mostly free of doing. We have stressed learning basic physics for the real world - mechanical advantage through leverage and gearing, basic electrical circuits, basic optics but with limited opportunities to demonstrate in practical contexts.
I had my kids change tires (summer to winter) on one of our cars, take the cars they were driving in high school in for oil changes, and have gone over the theory of operation of internal combustion engines and vehicle drivetrains with them. I haven't ever had to change a flat in their lifetimes, and the one major mechanical service item I needed done - replace a starter on my 4Runner - I had a shop due because I was too busy with work and life. I had to troubleshoot/repair an instrumentation failure in our Dodge Caravan that required removing the dash and re-soldering failed ground connections, but that was when they were younger and they got only a limited experience from that.
Compounding the lack of direct, repeated exposure to the basics is the fact that many people have a bizarre aversion to reading manuals (demonstrated from time to time on this forum). The result is that you get people doing things that seem to make sense to them but are less than best practice for vehicle repair and maintenance.