I've found the problems that biologists cause are mostly:
* Not understanding dependencies, public/private, SCM or versioning, making their own code uninstallable after a few months
* Writing completely unreadable code, even to themselves, making it impossible to maintain. This means they always restart from zero, and projects grow into folders of a hundred individual scripts with no order, depending on files that no longer exists
* Foregoing any kind of testing or quality control, making real and nasty bugs rampant.
IMO the main issue with the software people in our field (of which I am one, even though I'm formally trained in biology) is that they are less interested in biology than in programming, so they are bad at choosing which scientific problems to solve. They are also less productive when coding than the scientists because they care too much about the quality of their work and not enough about getting shit done.