In situations where there many diversions, sometimes secondary airports either get too busy to accept additional A/C or run out of space or crews to deal with them.

Sure, that makes sense. Does that likely mean there were other flights with even less fuel that had to land ahead of this plane, or how do they triage that situation? It seems like a failure to triage properly if one plane has to glide, but maybe I'm naive about how close all of the other planes are to gliding.

No planes had to glide.

My guess is there were too many other more urgent flights landing there at the time.