Why does this matter? Unlike heroes, we don't choose maps. They're queued in a playlist beyond our control. It would make zero difference.
Maybe they want an equal 25% chance at each game mode like we have now. If there becomes an imbalance towards KOTH maps because they release an additional two KOTH maps for example and no other maps, we would end up getting queued into KOTH maps 41% of the time, leaving the other modes less played.
They should probably release one of each of the 4 gametypes at once. So 4 new maps, 1 KOTH, 1 capture, 1 payload, 1 hybrid cap/payload, maintaining 25% chance at each game mode.