[captainbland]

I think it's largely a product of resources. There are fewer positions and more people who want to become research mathematicians so only those who are extremely well qualified even get to the post. The reason for the lack of resources is that the research mathematician's work isn't usually immediately profitable (hence their pay is often relatively low relative to their software engineering counterpart). By contrast, many companies operate their software development process in a way that allows them to recruit developers with minimal training and even deploy them in a way which they find useful, even if in fact that work might be completed more quickly by a smaller group of more experienced/capable programmers.

I think you're right about the pressure-free environment bit, too - some places developers are so bogged down with fire-fighting that planned development with real foresight rarely gets developed.

Moreover I think there are just more software developers, with much more variance in their abilities than research mathematicians.