I honestly have to ask, Why does this thread exist and how do posts here enhance it?

As several have said, it's an indication of stamina, and a limiting factor that allows jobs to have more powerful moves that'd be unbalanced if allowed to spam them.

Look at it this way: running a marathon is hard and requires you to not go all out, or you burn out. Conversely just because a marathon runner decides to run across the street doesn't mean they get to do that at lightspeed. You have limits on how fast you can dish out and how long you can dish out.

But that's all common sense, something you'd have to completely abandon in order to come up with OP's complaint.