I had an FA cut off the entire cabin last spring while flying Hawaii-PDX about 2.5 hours into the flight. Long story short, I called out the FA for making up the policy, as did others, and she was then overheard in the galley telling a Y FA that she was worried about being written up by the passengers, to which he replied, "Just say they were all really drunk and you'll be fine." I'm not sure why they don't think I'd hear that sitting 5 feet away... There's more to the story, but it ended with me writing in and receiving an apologetic call from customer care in Seattle.

The only other time I've seen it enforced was on an individual when someone kept ordering doubles and was cut off (they were becoming obnoxious).

I have seen a dramatic increase in FAs slacking off the last few hours of service on long flights. I'm wondering if this is to intentionally avoid offering refills to avoid having to enforce a limit.