That's possibly it, but I'd have thought the proximity to Leeds would have offered a good choice of roles within commuting distance.

There are presumably also fewer developers available in Harrogate to hire into that limited number of roles; especially because they also have the option to commute to Leeds as you say, or work for a higher-paying remote employer. Limited tech markets work both ways.

I'm based in Hull, which — like Glasgow — has a fairly low cost of living, and 28k for this still strikes me as incredibly low.