The entire Palm Springs/Indio California area couldn't shoehorn in another rig during peak season (January thru March) if they tried. My wild guess is the snowbird crowd is migrating more towards areas with many activities and attractions. The Palm Springs area has over 150 golf courses. There are casinos with top shelf concerts and entertainers. You are two hours from either San Diego or LA for professional sports and world class shopping. The weather is reliably spectacular each winter. Many of the same things can be said for the Phoenix/Scottsdale area.
The Rio Grand Valley, not so much. Reputation-wise it is pretty much thought of as the budget snowbird area. It conjures up images of pot luck dinners and shuffleboard. I think that area is finding that their market demographics is getting older because that type of snowbirding is not meeting the demands of the recently retired. And it might be a trend that is impossible to reverse.