I was hoping someone could shed some light on crew timeouts, apologies if this is discussed somewhere else:

Background: I was on a UA flight IAH>PBI on Friday (though i guess technically it was operated by sky west) and we were a little delayed by an incoming aircraft but probably departed the gate ~45 late, taxied out to the run way, were told we were 10th for takeoff and that it would be another ~30 min, after about 20 or so minutes the pilots said they had "timed out" and returned to the gate where hopefully another crew would take us...without getting into all the nonsense that followed and typical confusion and finger pointing, i was hoping someone could explain how this works, and the incentives.

My Thoughts/Questions : IAH>PBI is a short flight, and i know they had a return PBI>IAH after ours, but it really surprised me that ~1h+ delay would cause the crew to time out...the flight attendant said that they weren't going to time out on the way to PBI but rather the way back...which I assume meant that they had no back up crews in PBI so that that if the crew went, and got timed out, UA would need to cancel the flight from PBI>IAH (but it seems like that could have happened anyway if there was the tiniest of delays in PBI)

It seemed to me that the flight crew was pretty happy about getting timed out, does that mean they get paid for the flights that they would have had to do anyway?

If you're that worried about canceling a flight why not bring in a replacement crew right away instead of risking a high probability of it happening in PBI?