The length of the beta is likely a function of the number of features of the given app. I would think that most apps wanting to compete in this space would be u

The length of the beta is likely a function of the number of features of the given app. I would think that most apps wanting to compete in this space would be up against apps with insane amounts of features - think Adobe software - which would require a certain amount of time to test/fix per "feature". The same might be true of, for example, a Microsoft Office competitor. Lots of legacy functions tucked away in those apps. Just speculating since I've only personally tried fumbling around in Inkscape <5 times in my life, but it might explain the phenomenon.