When GA's get incentive bonuses for getting a plane out on time, they really care little about their customers, plain and simple.
If the GA's would just enforce the carry on limit that would help a lot. Earlier this week I saw someone taking on four (yes four!) pieces - a carry on, a personal item, a purse and a shopping bag. That really needs to stop. But GA's almost never care. I can remember only one time that a GA patrolled carry on items and made people condense or check a piece. Extremely rare (again, because by that time, it holds up boarding and the GA might lose their incentive).
Delta does not give bonuses to agents for a on time departure.