"A whole host of reasons" is a fairly common phrase to mean someone has a lot of reasons for a decision.
"Sea" is a bit less common, but you might say something like "he looked down upon a sea of friendly faces".
"Drove" is honestly one I would consider wrong, but only on a technicality. I would consider this sense of drove to be a "lost singular", in the way that "evitable" is a lost positive (from the real negative "inevitable") or "whelmed" is a lost form from under- and overwhelmed. You never see "a drove of" something, but you do see something "in droves".
I do agree with you regarding drove vs droves, but thatβs something Connections does sometimes. I think they sacrifice accuracy to avoid giving a hint (in this case that itβs more than one). I canβt name other examples off the top of my head, but Iβve definitely noticed it before.