Well... it's kind of a long story, but in a nutshell, they retroactively changed their third party content creation rules to take a firmer hold on their IP, which would dick over a LOT of smaller third party creators in numerous ways. Fans were outraged. Third party content creators were outraged. Subscriptions to their new D&D Beyond service started to get cancelled so fast they shut down the site. They've since walked this back, but the damage has been done.