Because it's better. That belief might be incorrect the vast majority of the time and/or in this specific case, but I for one am reluctant to quash that kind of enthusiasm. It's the fuel of progress, even if some (most?) of it is wasted. The disappointment and frustration of seeing "inferior" alternatives prevail are inseparable from the drive to create a better one. It's not about "owing" anything. For many people, it's about wanting to make the (technical) world a better place, being thwarted, and seeing the community as a whole diminished as a result.
Maybe some people don't feel that kind of passion themselves. Maybe they think emotion and idealism have no place in computing, though if that were the case I doubt we'd see so many flame wars. Maybe they've never had an idea worth getting that attached to, though I doubt that's a common factor in a forum for entrepreneurs. Maybe some people are in it for the ego boost themselves, and can't imagine others being in it for another reason. Whatever the explanation, the fact remains that some people do get invested in an idea for reasons besides ego, and it's good for them to do so.
Community, documentation are other metrics that matter a lot when choosing an open source solution.
If it weren't for that then everybody would be using Haskell or Clojure, those are so much better (at least, so I keep hearing) and yet the reality is different.
Beside the point. If your goal is to "beat" others (revealing choice of words) and either make more money or gain more recognition then sure, but not every piece of software is motivated by those goals. Somebody has to make the "better" even if they're not the ones to benefit, and many are fine with that. That's particularly true in open source.
Assuming a particular motivation for the OP, and then insulting them based on that assumption, is just wrong. In fact, I think some might even see it as hitting someone when they're down - i.e. bullying. People who've gained some prominence in the community should try to do better.