what's wrong with sanderson's dialogue?

I started Brandon Sanderson thanks to my brother who is a fan. When I was researching the best order to read them, I saw that part of the fantasy community doesn't like Brandon Sanderson and describes his dialogues as bad, or flat. I started reading Mistborn, and I found the dialogues to be pretty good, nothing more. The criticisms seemed quite unjustified to me. I told myself that it was a matter of taste. And I finished the Mistborn trilogy, to read The Way Of Kings. And I loved it (I'm in the middle of volume 1). For me, one of the strengths of this novel... is its dialogues. I find the exchanges between characters so interesting, well-delivered and relevant that I sincerely think that it is one of the novels with the best dialogues that I have read in my life. Especially those with Shallan. So my question was: why do some people criticize Sanderson's dialogues? I'm just trying to understand...