I totally agree I am so confused by this whole thing
A lot of times, it's more than being a World champ that drives kids to go elsewhere or return to wherever it is they switched from:
*Homesick. Ex: You may have gone from Cali Smoed to being on Senior Elite or whatever and that's great, but there are things you'll miss in CA that you don't get repeat opportunities to experience. (ex: your best friend's graduation is only a one-time event.) So you decide to move back to your home gym (Cali) to be closer to everyone.
*Coaching staff. Yes, being on (example again) Senior Elite seemed AWESOME when it was just a dream. In reality, you don't mesh well with the coaching staff, and you really would like to go back to Smoed where you KNOW you mesh with the personality of the staff.
*Testing the waters. Nothing in cheer is permanent. So you decide to "take a chance" and try out for (example) Senior Elite by video. The worst that can happen is that you hate it and you move back. This is year-to-year commitment and I think people forget that.
*Teammate personalities. You thought you'd mesh well with all of your cheer idols on Senior Elite. You now realize that all is not what it is cracked up to be and you personally don't enjoy spending 20-30 hours per week or more with them.
*The opportunity becomes unavailable. Let's say you try out for Senior Elite. That is what you wanted. So you try out via video and make it. Now, in August, the coaching staff has decided you're a better fit for Lady Elite. Hey! That's not what you tried out for. So you spend your year on LE and go back to Cali.
*Money. Yes, being a Worlds athlete is expensive. It is more expensive to be a "living out of state" athlete. Sometimes, your parents thought they could swing it but they can't.
Again, never done it but I'm sure the reasoning is similar to why kids in other sports move back and forth.