What do you mean? It works every combat

But you can only take the Technique once. It originally said you could take it multiple times and get more back at the end of the encounter. Then, they cut it to one take only.

Because it could easily be the BEST Force Technique to take so that none of the others would ever get used. If we asked why one is concerned they could only take it once that may answer your own question.

I may believe encounters run longer than others and thus might include a number of related fights and even then being able to get back X FP each time is big. If you go with every skirmish being it's own encounter that is completely unrelated to that fight you just had in the last room and the one behind the door into the next room it is absolutely NUTS to get back multiple FP each fight.

Summary: In large part because of Power with really was hurting diversity.