>which [why?] is this suddenly a problem?

Because most of teachers didn't teach online class before. They are not used to design exams that would not be way too easy it suddenly becomes open book.

I won't even say they're "lazy", coming up good take-home exams is super hard, especially when you spend your entire career not need to do that.

> if people want to cheat they can find some way to cheat regardless of any countermeasures you deploy.

I agree if it's online exam, it's kinda doomed either way. But it's more to act as a deterrent than total solution. And it does work to some "less-adventurous" students.

Note: above is just directly replying to your questions. I don't support scanning student's room.