Unlike with radiologists, being a software developer isn't really a career, so looking at BLS numbers doesn't make much sense. Asking how much a software developer should make in a year is like asking how much a telephone user should make in a year; it's a nonsense question, because clearly there is almost nothing in common between someone doing low-level tech support and someone selling stock for an IPO or whatever.
The reason most software jobs pay less than most radiology jobs is because developing your radiology skills doesn't come with a potential billion dollar upside, so people aren't willing to do it on unsustainable terms.
That's not a good explanation. Very few employees will ever see billions of dollars and clearly the people taking jobs at big, established companies aren't doing it out of some hope that they'll suddenly become billionaires (how would that even happen?).
The reason most software jobs pay less than most radiology jobs is because developing your radiology skills doesn't come with a potential billion dollar upside, so people aren't willing to do it on unsustainable terms.