Frontier Airlines EarlyReturns - aircraft usage

i've noticed quite a bit of aircraft down time around the F9 system. we always hear about planes only making money when in the air, so i'm a bit surprised F9 can't manage increased usage.
some examples:
*redeye DEN to BWI sits for 4 hours before returning to DEN.
*TPA overnight arrives 1055pm but doesn't depart for DEN until 9am.

Seems like this may be due to a few different factors:

*Lack of gate space in Denver

*Connecting "banks"

*Crew rest - on the TPA turn, it looks like the same crew probably brings the aircraft back to Denver

*"Head start" - this refers to the first flights of the day leaving on time - the BWI and PHL redeye flights from DEN often hold for late connecting flights inbound from the west coast; while this usually doesn't result in much of a delay, if the turn were scheduled for 40 minutes in BWI, it could potentially throw the schedule off the next day as well.