What's not clear to me is why MS implemented the "protected folders" feature so half-assedly as to be useless? To me, the important thing to protect on a compu

What's not clear to me is why MS implemented the "protected folders" feature so half-assedly as to be useless? To me, the important thing to protect on a computer are the user's files. Instead of regularly scanning everything and comparing to known bad signatures and grinding the machine to a halt, why not limit what the apps can do? If it's hard to prevent users from downloading totally_not_shady_app.exe, just make sure that it can't access anything anyway. That may still allow it to mine bitcoin, but at least it won't leak sensitive data. Or better yet: most users aren't devs. Just don't execute anything from the users' home folder. This probably won't help with all the attacks on Office by macros and whatnot, but it'd be a start.