This would also lead to safer cars because they are better roadworthy
Well, I'm not sure about this literally about car and figuratively about selfhosted: not all the selfhoster have the skills to selfhost, they just think they have and so for the car. If you screw up a service/the whole server you may lose all your data or be at the mercy of some data kidnapper, if you screw up your car brakes, well...bye bye.
In both cases, we don't have enough skilled people to have that 25% selfhoster (but not even one tenth) nor 25% car self repair drivers. And this is not as bad as it sounds: we can't be skilled about everything that we need, it's just impossible! And that's why we have society!