Well, there is a reason for that; WB doesn’t have full ownership of Harry Potter or LotR. The licensing agreement with Tolkien’s estate means that works like The Silmarillion are off-limits, and WB tried to get a Cursed Child adaptation made, but JK Rowling said no.
Anyway, the fact that Zaslav is so desperate to turn WB into a dollar store version of Disney is especially lame, because Disney isn’t even doing great right now.