When you put to many forever loops especially in scrolling platformers, it slows down the game

This really isn't that much of a glitch. It just means that the computer can't handle a bunch of forever loops at the same time.

Your computer has a limited amount of things it can do at a time. As you get closer and closer to the max, your computer starts to slow down. The more loops it has, the longer it takes to do each one.