The selling point of cold brew is that it is less bitter tasting. Which means it's not a surprise when there's less tannins/antioxidants in the liquid.
It's a bit surprising to me, because I assumed the difference was merely due to temperature (try to drink soda at the same temperature as a hot cup of a coffee, I guarantee you won't like it)
Coffee is actually not supposed to be bitter and has more aromatic compounds than wine. The bitterness in commodity coffee comes from overroasting and overextraction.