It's a little difficult to figure out the origin of this one. It's incredibly common, and a lot of rings certainly look bouncy, especially on independent shows, but they also look nothing like trampolines. Have you ever seen kids try to wrestle on a trampoline? It's not pretty. They're tripping over themselves. The closest "real world" analogue to what a wrestling ring feels like is a gymnastics spring floor. It's hard enough for you to easily keep your footing, but it has enough give that you're not landing on concrete. That's why taking a bump is like a small car crash: You're still landing on a hard surface, it just moves a little bit when you hit it. WWE has built a "high flying ring" that's used at the Perfomance Center in Florida, which is a regular ring except with a platform in the corner and a crash pad-like surface. You can't have a match in it, as it's designed solely to practice flying moves in without taking damage. Maybe, over time, they'll find a way to build a more forgiving ring that has better footing.