I first started disliking him after that interview where he and Paolini harassed Robin Hobb, but since then I've noticed that:

• he enabled and continues to enable Paolini's worst traits as a celebrity author
• he's the king of the fantasy dudebros, which is a subset of the fantasy community that has a reputation for being toxic in various ways, notably the exclusion of non-male, non-white, and non-straight authors from their in-group
• he opposed marriage equality and gay rights because of his religion, until he had a financially-convenient change of heart right when his earlier comments might start to affect his book sales
• he wrote a pro-Zionist book set in modern-day Jerusalem (and even visited in 2019 to give a talk) that paints the Palestinians as violent terrorists and the Israelis as the peace-loving victims only acting in self defence.

Plus I wasn't thrilled with the attitude and manner in which he took over finishing Robert Jordan's Wheel of Time series after Jordan's death, and then positioned himself as the authority of the series for the Amazon Prime show adaptation.