I work in an research setting with access to lots of skilled software engineers and I've come to a very similar conclusion. The problem I often see is that there is very little incentive for the researcher to bring a software engineer onto their project unless it is absolutely necessary. It is just now becoming commonplace to release code when you publish and plenty of researchers still don't.

If you think no one is going to see your code then it makes it much harder to care about its quality. One way we've been fighting this internally is by trying to get researchers less silo'd and more open to code reviews. Once a code review is part of the process then bringing on an "expert coder" to address some of the issues that come up in the reviews has more tangible results! We've seen some success in improving our code quality with this strategy.