I am a big fan of open source code. I think I understand most of the advantages of going open source. I'm a science student researcher, and I have to work with quite a surprising amount of software and code that is not open source (either it's proprietary, or it's not public). I can't really see a good reason for this, and I can see that the code, and people using it, would definitely benefit from being more public (if nothing else, in science it's vital that your results can be replicated if necessary, and that's much harder if others don't have access to your code).

Before I go out and start proselytising, I want to know: are there any good arguments for not releasing not-for-profit code publicly, and with an OSI-compliant license?

(I realise there are a few similar questions on SE, but most focus on situations where the code is primarily used for making money, and I couldn't much relevant in the answers.)

Clarification: By "not-for-profit", I am including downstream profit motives, such as parent-company brand-recognition and investor profit expectations. In other words, the question relates only to software for which there is NO profit motive tied to the software what so ever.