According to a report from Gaming INTEL, it seems that Treyarch will be taking a radical approach with Black Ops 4, where they will be doing away with traditional multiplayer season passes. There are some apparent reasons for this, one of which has to do with Treyarch trying to maintain a steady player count.
In the past it has been found that the player base tends to increase following the release of new maps, but then falls off later. However with a steady release of 1-2 maps a month, Treyarch might be hoping to avoid this kind of see-saw movement in their player base. It could also have to do with the Blackout battle royale mode where Treyarch is hoping to keep the matchmaking pool big.
This is because when DLCs are released, the player base gets fractured between those who purchase the DLC and those who don’t, so by keeping things equal, they can ensure that there will always have enough players for the battle royale mode. Take it with a grain of salt for now, but so far Treyarch hasn’t confirmed anything regarding DLCs or a season pass yet.