On Topic: Whatever happened to the fat, jolly Kevin Smith? This can't be the same guy who brought us Clerks, Mallrats, & Dogma.
Some people see their best creative days behind them and are unable to recapture that spark. Others can return to form but after a creative dry spell. No one can be Scorsese or Tarantino, and no one is to blame for this.
This, however, would justify a bad MOTU. The problem here is that Kevin Smith destroyed the premise of the show, lied through his teeth for months after the fact was leaked, and assaulted the fans with swear words when unusual questions like "Why He-Man isn't in the 'He-Man' show?" were made. It was a mini-The Last Jedi all over again.
[Admittedly, Netflix lied too, during the propaganda phase of the launch.]
And from what I hear the show is bad, too. As usual, there is no reason for something that doesn't respect the source material to be bad. Kubrick did it all the time ("Doctor Strangelove", "Barry Lyndon", "The Shining"...) It could have been a disappointing He-Man show but a good Teela one. These days, however, this never happens.
Edit: The fact that Smith still dresses like a slacker from the 1990s is, IMHO, the proof that he is unable to grow out from that period of his life. It would be interesting to hear what Kevin Smith has to say today, but I fear that he never reached "today": he is still trapped in the times when he created his best works.