I suspect this is a new tactic of being extra nice to the few people renting the small, old fleet at high prices. The rental companies will need to hold onto them, since this is a market segment likely to still rent no matter what.

Everyone else is starting to get tired of booking vacations and being surprised by astronomical rates, thus learning to plan trips that minimize the need to rent cars. Once consistently cheaper alternatives are found, behavior may not switch back to renting, even if availability improves and rates go down slightly.