Very often they are making less than a career in a lucrative field would bring but still more or at least equal to a median job. And they have a lot of benefits that are just not very easy to put a price on (freedom to do what you love is priceless for some).
I think there is a distortion coming from the "bottom of the barrel musician" that spends way too much time complaining instead of trying to improve (or moving on to something else if they don't have what it takes). The reality is that the vast majority of music produced/performed is so bad it has absolutely no value commercial or otherwise.
I don't think the software craft is very comparable, it's just not the same incentive and constraints at work...
On a US national basis it is basically true. Median weekly earnings for full-time workers is $1,192[1]. Median hourly pay for a software developer is $62.58[2], which, assuming a 40 hour week, is $2,503.20.
[1] https://www.bls.gov/news.release/pdf/wkyeng.pdf
[2] https://www.bls.gov/ooh/computer-and-information-technology/...
That may not be a fair comparison to the extent that software devs are concentrated in high CoL areas, though, so you don't see a ton of us out in the cheaper and poorer regions. The effect of that is somewhat ameliorated by taking the median instead of the mean, but not fully.