Factor in also that the F cabin usually has more seasoned travellers than Coach does, and PAX don't always recoginze that it's not a good time for them to stand up even if the FA's stand up. FA's are used to walking around in the chop and your casual traveller isn't; they just know if someone else is walking around, they want to as well, regardless of whether the seatbelt sign is on or off. Keeping the FA's down in the back of the plane keeps more PAX down too.

I really don't see anything wrong with this. Keep the cart out of the aisles, keep the PAX seated.