In addition to what my sibling comment says-- there's a whole lot of draws by agreement because the position is one that everyone knows becomes draws by insufficient material.
Sure, but there's also a whole lot of draws where insufficient material is inevitable. E.g. pawn vs nothing, where the king cannot reach the pawn to defend.
And there's also draws where the only move "forward" doesn't weaken the position, but lead towards an end of insufficient material. E.g. most situations pawn vs. bishop.