Ben Affleck didn't want to do a solo movie anymore, thus he dropped out and the reason why WB when ahead with the new reboot which was due this year, but pushed to 2021 with covid. It's not a case of WB not wanting to do a Batman movie, as they are making them, as well as putting Batman into everything they can at the same time.
WB put out Batman Soul of the Dragon, Batman Long Halloween Part 1 and 2 in this year alone, they love to milk Batman. Also, Flash movie has both Batfleck and Micheal Keaton in it, you are likely right about it not being much screen time, but it shows how WB will put Batman anywhere they can. They also got Batman spin-offs, like Joker 2, Batgirl and a Gotham City Police Department show in the works.
The only way WB could have got a Batman movie out faster, was to force Ben Affleck to make the one based on his script or to fast track one without time given to make sure it was any good. Lots of shit you can give WB, but the lack of Batman movies is really not one of them.
Superman is different, while they are milking the hell out of the brand, they never tried to do a Man of Steel 2 in any way, despite the cast from my understanding still being up for it.