The FAA requires one F/A per 50 passengers.

That's why lots of planes seat 100 passengers or 149 passengers, etc. to get the maximum workload placed on each F/A.

I don't think any airline has "extra" F/A's.

They work hard and dealing with the public has to be challenging, especially with all the service reductions that various airline management teams make. The F/A is the one who gets all the complaints and is hassled for decisions that someone else made.