I think the argument that it is taxpayers money that paid for the software is more persuasive.
I am a research scientist who does a large amount of source code development. Sharing that code is only infrequently useful to either the public or other scientists.
The reproducibility argument is a weak one. The methodologies are described in any paper worth its salt so the software could be (and often should be) rewritten independently. Indeed such a rewrite is a better test of the original results since large codes are hard to rigorously assess if you did not write them. Since the algorithm is published the software SHOULD be reproducible.
On the other hand it really helps the scientific community in general if codes are shared. It can often save a lot of time.