It’s a common problem with lots of classic sci-fi authors. Heinlein, Asimov, Philip K Dick, Larry Niven etc. are all terrible at writing believable dialogue and compelling characters. There are some exceptions, but most of their characters are cardboard cutouts so they have a way to move along a story or give exposition about the ideas.

The Expanse did a pretty good job with characterization (in the books), and Kim Stanley Robinson is decent (but is still pretty “hit or miss,” IMHO), but in general, the weakest part of sci-fi writing is almost universally characterization and dialogue.