GTVA can't deploy too many destroyers mainly for logistic reasons. I don't know how many Anemois they have, but by the looks of it, not nearly enough to pour the kind of forces they'd need to finish the war without weakening the rest of their territory.
Given the overall policy of the GTVA aside from the Sol theater, ie defending a known and controlled territory, I guess Anemois aren't exactly on the priority list of destroyer-grade hulls to produce. It looks like those things aren't exactly cheap either (as you would expect from a destroyer-sized vessel filled with expensive spare parts). If you assume that less than 1/4th of the Anemoi is used for spare parts, you still have 100 millions m^3 to fill. Just saying.