I never thought of that as being strange. I think it's used this way because it fits with "a few," you know? "I had a few drinks," "I had a couple drinks." But

I never thought of that as being strange. I think it's used this way because it fits with "a few," you know? "I had a few drinks," "I had a couple drinks." But fwiw, "I had a couple of drinks" doesn't sound wrong to me.