You're right that it should be easier to replace a phone's battery than your car's, but it's not $50 for the tool, it's $50 for the factory battery from Google. The kits basically get tossed in more-or-less for free.

Also, it really doesn't take three hours to swap a phone battery, even in our sad state of planned-obsolescence affairs. That's pretty extreme. As I wrote elsewhere in the thread, I did an iPhone and an Android last year and each took less than a half hour. The iPhone was fiddlier, but it was also the first I'd done. The Motorola was surprisingly forgiving. But I agree, gluing mass-market devices together is bonkers and only benefits the manufacturers.