Crawford is not being relied on for his defense, that's for sure. That said, he brings more to the table offensively than Lee currently, which is why his number is getting called over Lee's.
I would say overall, Bradley is a more balanced player than Lee. Lee's ball handling/passing is arguably just as good as Bradley's - if not a hair better. Bradley is a better defender. Both are struggling offensively right now. Given that Bradley's skillset slightly outweighs Lee's, Bradley is getting the nod to start. He's also been on the team longer and probably knows more about Doc's rotations/plays.
What's left for Lee to do? Score. Which he has been incapable of since the end of the regular season and all of the playoffs, unfortunately. I had higher hopes for him too. I think the pressure has gotten to him