I think part of it is funding--but part of it is also recognition. In a number of fields, the development of scientific software receives little recognition co

I think part of it is funding--but part of it is also recognition. In a number of fields, the development of scientific software receives little recognition compared to the science--even if the impact is large in terms of the discoveries it enables. So, for say tenure or career advancement, it might be "nice" for you to do it, but nowhere near as important as publishing high impact papers (at least in many fields). Especially if a graduate student or postdoc commits too much time to it instead of research results, they risk not being able to continue in their field (though they probably have more options if they decide to leave science to become software developers).