DnD 5e had a license for use that allowed 3rd party companies to make stuff for the game following specific rules, and they did so which of course helped with increasing the popularity of the brand. This license existed due to the backlash from players and 3rd party developers who did not like the 4e licensing which was ridiculously restrictive.
Then WotC/Hasbro decided they wanted more control and put out a draconian revision and also tried to invalidate the existing license using questionable legal logic that wouldn't stand up in court, but would be cost prohibitive for the 3rd party companies to fight in court. This revision also included licensing costs that would drive 3rd party companies out of business. Then they did a revision that tried to make creating a virtual tabletop that could be used with DnD a violation to try and corner the market for WotC's completely non-existent virtual tabletop.
Basically they tried to stop doing the thing they had in place for like a decade to milk an unrealistically high amount of money out of companies that were working with them and tried to force this on extremely short notice. So same thing as reddit and now Unity are doing.
Expect the next version of DnD to be a walled garden again like 4e was and most likely fade out of the public view again.