Why can't edit our rune pages in champion select?

You can, you just have to be sneaky about it. Edit some of them while you're in queue. But don't save. Then after you get into champion select, it'll ask you if you want to save. Wait until you've seen some other picks and things people have said and then choose one of the options. If you were in queue long enough, you can essentially double your rune pages. If you get into a match really fast you can just decline it.

But anyways, they make money off of rune pages so they wouldn't do this since they'd make less.

If you could, why would you buy so many rune pages and how would Riot make up for the lost profits?

It's all about the LC$

The player has to make a choice between optimization and flexibility. I'm fine with that.