Some operational insight
Load planning and held seats:
Central load planning has a department that handles the common weight restricted flights. SNA-EWR is one that is looked at daily. This analysis will start up to two days prior and looks at NWS forecasts, booking loads, cargo, burn, etc. They pass their recommendations on to dispatch and sales to hold seats. This analysis is repeated until closer in. It typically ends early the morning of. The ball is now in dispatch's hands.
Variables: Unexpected temperature forecast. Longer then tradition route due to ATC enroute or terminal restrictions. Unexpected alternate airport requirement or further alternate due to convective forecast. Dispatch will try to minimize fuel uplift. They will release the flight 2 hrs prior, in the case of 1559, around 10AM. This is still based on the forecast for temperatures at 12p-1pm. If a flight gets delayed later to the afternoon, temps will go up. When crew gets to the plane, they will pull takeoff data for current wx conditions, and likely found the temp quite higher then dispatch forecast from 2 hours prior. Loadplanning and customer service will not know this tighter restriction until dispatch reruns the solution on their end, probably 30 minutes before departure.

Defueling or "tech-stopping" at another airport.
This decision gets bumped up the command chain in NOC. Typically to Ops Managers who make the decision. Defueling requires a special truck. In a hub, it is dedicated to United and we can typically reuse this fuel in other aircraft. Process takes about 1hr from first call. At a non hub, fuel is considered contaminated and can't be reused. The dedicated truck/driver with defuel training takes quite a bit longer to source. I would speculate 1.5 hrs minimum. From an operational integrity standpoint, it is almost always better to remove revenue unfortunately.