Why not? Why not 1 instance per hour? Why not 1 instance per day? What is so sacred about the number 5 that other numbers are not compelling?
Is it “no changes”? If so, there was no instance cap for a big part of vanilla and there was certainly no 30 instances per day. I think it’s pretty safe to say that no changes doesn’t apply here.
Is it your flimsy pretext of server stability? You have already conceded that it probably isn’t that.
What is it then? Why is 5 such a magic number that you can not possibly conceive of any other value?