Why are people just accepting casters taking forever to pick their spells?

As a GM, I'm not. You pick your spell on someone else's turn, and be ready for action on yours!

I like it even less if they ask me what their spell does or need to look it up in their turn. No, you're casting something else at that point, and look up that spell for your next turn!

Of course, I do communicate this, and some other things, beforehand.