While most providers offer CBJ or BBBJ, I’ve found that almost all providers are willing to BLS bare. If you’re already down there licking and sucking my nuts bare, why not just suck the cock bare too? (Is it a medical thing?)

Because you're not going to get bodily fluids in your mouth from licking someone's balls.

So even if you don’t CIM, the possibility of precum is enough to deter BBBJ for some? I always thought it was a matter of taste or whatever but that makes sense.

Agreed.  I do BBBJ but no CIM, excessive pre though will warrant a cover.  Exchange of bodily fluids to me is a big no...  I want to stay clean and be able to offer that cleanliness to my guests