As I think back to my nearly 1000 nights spent in various Marriotts, I don't remember ever being directly notified by a hotel before I arrived that their pool is down for annual maintenance. And I have had times where the pool has been down just like the OP is dealing with. But in all fairness, they have always provided use of a different pool at another hotel. I do agree with the OP though that that can be problematic to use especially if the weather is cold outside. I wonder how many, if anyone, actually goes to the different hotel to swim in its pool? I bet the number is very small as it is definitely a big inconvenience.

In all those times, I don't think I ever asked for any "compensation". But I do seem to remember a couple of times, the hotel staff offered free breakfast, or a suite room upgrade or something similar. Those were probably times that I had planned on using the pool and commented to the staff about it being down with no previous warning. Considering that Marriott has an email address for me, and most every reservation I make has that email in the reservation, there isn't really any reason the hotel couldn't have sometype of automated email sent out to let people know.

Note that there have been times that I have stayed at some hotels where the pool was down due to renovations. And virtually every time there, the website had a notification of such. In fact, quite often in those cases, the reservation itself even mentioned the renovation information, just so I wouldn't be surprised.