I don't know why it's fortunate (or matters) that tower PCs are getting rarer, I still find it hard to beat a traditional tower if one needs a powerful and easily expandable machine, though obviously with components shrinking these don't have to be as massive as they used to be.
Fortunate, because tiny computers, should take much less resources to produce, than full sized ones.
If you want to have a 64 core monster (AMD threadripper) computer, with water cooling, multiple oversized graphics cards, many disk dirves/SSDs, and huge potential for expansion. Then, a large tower case is still the way to go. (I know even threadrippers can be achieved in small cases, if you want to go that route).
But these days, a mini sized computer can still be rather powerful, for most things, people do, 99% of the time.
I'm NOT clear, if a really tiny mini-itx computer, can be as reliable and long lasting, as the full sized desktop equivalents. But, if it achieves decent cooling, and you don't go for too high a wattage cpu (these days even 8 cores, can be rated for 65 Watts, or less), it can theoretically be done.
Cars are a bit different though, to a point the physical size of a car is dictated by the stuff you want to fit inside it. For a commuter car or for a single person without a lot of stuff a very small car is probably fine. Many of us need something a tad larger, I don't need or want a gigantic SUV but I love my station wagon and I utilize it very frequently for transporting large objects, camping gear, materials and supplies, etc. My little brother has a Fiat Abarth which is a great little car but since he has gotten more heavily into photography he's finding that he can't fit all his gear in it. Somebody with a few kids is going to need something larger than a subcompact to comfortably haul around the family, especially if the kids are into sports, band, or other common things that require some cargo space. Very, very few people need a huge SUV though, I'd love to see the return of proper station wagons, they are the perfect practical car for people like me. Loads of interior space, highly versatile, yet no larger footprint than a regular sedan. Sadly they are all but extinct.
I agree. Some people, need certain capabilities, from their vehicles. But many people, seem to have giant vehicles, without any real life NEED as such, and don't even go off-road, ever (as regards what we call 4 wheel drive, in the UK or 4 X 4's). I.e. Range Rovers etc. (SUV in US terminology).
Even if you need the massive vehicle, perhaps the planet can't sustain the resources needed to create it and keep it on the road. So we need to limit, who has them.
tl;dr
Somehow, we need to keep people 'free' and choose how they go about their lives. Yet keep planet Earth running in a smooth, efficient and sustainable way.
Maybe there is a Nobel prize, for the person who can solve that problem.