they've had it like that for a long time already and I had made issues out of it before on this forum.
I don't think they'll take away the guaranteed late checkout benefit for elites anytime soon,,, but i've noticed that often Marriott makes these messages vague on apps/websites,, potentially in the hopes that some elites, who are less familiar with program T&Cs, will take that to be the rule and accept being denied a late checkout.

to be fair, it's not only Marriott that plays with words like this...