Batfleck is universally popular. Look how social media went wild at the announcement he'd appear in Aquaman 2. Virtually everyone fully embracing Batfleck. If a similar announcement had been made about Cavill the social media reaction would not be near as great and it would be controversial. Most seem to be meh on Cavill but there is a vociferous anti-Cavill group who don't want him near the role again. There is also a vociferous group on the other side, with my experience being that the former is larger than the latter. Cavill's reviews were poor for MOS. He was seen as wooden in the role with no natural charm as Superman. A charm Cavill has in interviews, but which did not come across when he played Superman. Zaslav has access to the audience polls and Cavill did not fare well in them. Strike one.
Cavill is too old. Zaslav wants to start from scratch which means a young actor who can age into the role over 10 years instead of one who is already aging out of the role as reportedly WBD feels. Strike two.
Cavill's salary and other demands. The only one in a position to make demands is Zaslav. Strike three.
Affleck is different and that is obvious from what has been going on in recent weeks. My bet is that Affleck has already signed a contract and his planned solo Batman film has been greenlit. Stay tuned. If WBD does a Fandome look for it to be announced there.