The one of the common ways for someone to get their (windows) computer hacked is to get tricked into executing a .exe file. Hey why not block programs unless they are approved by windows? Let’s call it Windows 10 S, S for Secure! (/sarcasm)
I mean maybe we could compromise a bit and hide the sideloading behind the developer options. Not connecting to a computer and ADB, just behind the developer menu. Most people don’t even know how to get that menu, and the people who sideload will either already know it, or can easily find out after a quick internet search. As long as there is an option, I’ll be able to find it.