Really? I'm doing a Ph.D. in sci-vis and my experience has been that people don't release code. One time I emailed a group asking if they were going to open source their code (and asking questions about some parameters that were unexplained in their paper) and a week later they responded by telling me to go the tutorial page on pytorch (seriously.... just ghost me if you're going to pull that kind of crap). It seems to me that a lot of groups keep code as a "secret sauce" per-say. Personally I feel that's anti-scientific, reproducibility is a fundamental element to doing science.

Big and famous groups/companies usually do release their code nowadays.

I'm automatically suspicious when someone doesn't, even though I guess most of the time it's nothing nefarious. It's just extra work and effort to bring the code into presentable shape and that effort could be spent on the next paper. Once the paper is published, the material benefits have been reaped, publication count incremented. Of course this is a short-sighted view, because in the long term not only the paper counts matter, but also one's general reputation within the community.