Why are the Tactical Team, Science Team, and Engineering Team apparently the same people?

Wouldn't there be a team dedicated to just tacitcal...a team dedicated to just science...and a team dedicated to just engineering?

My point is...why does Engineering Team put the Tactical and Science Team on cooldown?

If you listen to the FX made when you activate one of them, they use the transporters on your ship. And I imagine you are sending/using LARGE numbers of crew when you activate any of those abilities. What the cd is caused by are the transporters being prepped for usage again.

I guess that's a way to look at it.

Though I thought that the crew were always at their stations...especially when on red alert.