24 hour fitness got sold about a year ago to a private equity group and most of the purchase price was in debt financing. It wouldn’t surprise me if they are trying to boost revenues in this manner.
Your new rates are still probably still 3 or 4 times lower than what a new member would pay and at $4 month if you actually used it it was an incredible deal.
This reddit post seems to indicate in the fine print they can indeed do this and they have been doing it.