If a big car parks next to a big car, they have less room between doors, so it makes sense to park a big car next to a small car so they have more room to get out.

Where I live everyone seems to own 4wds but the carparks aren't designed for them, so it's difficult. I only get annoyed when the really big ones park poorly & if there's one on either side it's near impossible to get out of my park. Although it's a running joke that the biggest vehicle always parks next to me!!
I carry a piece of pool noodle with a cut in it to place on the edge of my door to prevent damaging someone else's car because they've parked so close I can't avoid touching their car.

I think if I drove a big car I wouldn't understand your question but I also struggle with this and will be getting a SUV for my next car as I'm sick of having to blindly back out as there is no way to see past the SUV parked next to you.

Because they just don’t care. EVeryone is in a rush and they just see a spot and go for it