This aspect of the MR program has been in place the whole time.
Traditionally, in the US, the lounges are closed Friday afternoon and reopen Sunday evening. And the free breakfast/lounge access has always been just for Monday through Friday. Sure, some countries/Marriotts have lounge open on the weekends, but not so much in the US.
It's just standard practice. I personally think this is one thing that Marriott will never change - it's been in place too long.
Sure, it would be nice to get free breakfasts (especially at resorts) but I just don't see that happening.
Billy