DC Universe is only about a year old.
Before that Warner Brothers wanted to get revenue from non current DC movies and shows and signed contracts which gave other streaming services an exclusive liscense to that show. Many of these comtracts will be in effect for a long while.
DC Comics was not always part of Warner Brothers. For example Batman 66 TV show is owned by Fox which is now part of Disney.
Exclusive rights to Batman.and Swamp Thing were given to producer Mike Uslan in.1979 and 1980.
There is a unit in.Warner Brother whose job is to maximize revenue from these films. They gave out contracts to these films which caused films that were hete to be rotated out of here. Once HBO Max comes on line in May that will no longer be allowed.
HBO Max will have exclusive access to all DC films from the last forty years. Whether HBO will share snything with this sister site is unknown at this time.
Shows like Watchmen Sandman and Green Lantern.are too expensive for DC Universe. Other streaming services have million more subscribets and charge twice as much monthly. So they have the resources
See
And the posts below it for further details.