Being related to a couple of FAs (in the top 1/3 of the top 1/3 of the top 1/3 in seniority), I know it really depends on the time of day, the route, (who they are flying with), and what the current service levels are.

F has gone back and forth in the level of service and complexity. Also, the FA in F is also "in charge" and gets some additional responsibility and more pay. That trade off plays in as well. Some just don't want the extra stress if anything does go wrong or there's an issue in the cabin or a delay. They also have to make the announcement, and I'm sure some love that and some hate it.