How does "flow control" work when planes dispatch from the same city into the same destination, and they're scheduled departure times are two hours apart?

Once the hold lifts, shouldn't the plane held for three hours at the gate have priority over the one scheduled two hours later?

DL 2094 actually pushed back a bit early (LAX-ATL) today, while DL 2092 - already into a three-hour hold - was still there. And would be for hours more.

Why would dispatchers leap frog like that? A redcoat called the tower and was tersely informed, "It happens, sometimes."

There were NO apparent crew rest or mechanical issues, just somebody deciding to get creative as 194 pax lost the dispatcher lottery. I hate to think how their frustration might have been manifested had those flights left from adjoining gates.