That's... not how it works. Studio systems and long spanning film contracts are complex. Once you've a partner in a franchise, it can be very hard to extract without it being really messy or a total fallout. Snyder and his wife are producers on not just BvS and JL, but the entire DCCU slate. Their company is overseeing everything on behalf of WB, and the entire slate is based on work they've mapped out and deals they've arranged with the various directors and so on.
If they want to remove Snyder from the equation completely, they would have to scrap everything and start over. Everything. It would mean not having a new film after Wonder Woman for possibly several years. No way they will do that. There's a reason even Goyer is still an Executive Producer on BvS. Once you're part of a project, it can be hell to completely remove the person.