Beyond creative input, there's also the question of liability in case of academic misconduct. I'd question if someone acting in a technician role (say a programming professional) would have a full understanding of the manuscript and so could accept authorship; they may also lack the ability to check the findings of the manuscript which is also problematic.
> If you successfully take an idea from concept to working software, or if a research project requires complex software to be written, I think it is almost inevitable that the software developer will end up making a creative contribution.
I think we need to be careful about how we define creative contribution; there's a line to be drawn somewhere in there between a creative contribution for the sake of the software (i.e., speeding up execution time by 4x for a simulation running on a cluster) versus a creative contribution that enables the research (i.e., a novel real-time optimization algorithm for electrostimulation). The latter certainly warrants authorship, but I don't think the former does.
> I'm also a bit suspicious about the justification that you can't be listed because aren't a "scientist". Of course, I don't know the details, but it seems fishy.
Ditto, which is why I asked. My first thought was that it sounded like scholarly authorship was poorly explained and if so I was hoping to help out with that.