Real easy answer: keeping a fridge cool during a very hot summer outside requires a more powerful cooling system. Instead most people have a powerful AC since you want the house cool anyway, with a cheaper fridge cooling system

The reverse is also true. You wouldnt want your fridge to require a heater installed in it to keep your food from freezing in esspecially cold winters

KDE is commited to keeping the desktop itself SystemD agnostic. Their new login manager does depend on SystemD, but you can run KDE Plasma from any login manager

SystemD isnt exactly a program but more of a group of projects, the only “core” SystemD software on most distros is the init system… Which you can run completely without SystemD’s UserDB system (the part being talked about in the post).

Basically this means you as a user dont have to do anything but switch away from projects that depend on SystemD’s UserDB (like Gnome), not SystemD as a whole

However if you do want to move away from SystemD as a whole you can replace your init system with another one, gentoo’s wiki is a good starting point for learning a bit more: wiki. Personally I love using openrc but of you have no need to touch init files… Dont switch