Nothing, but our industry is driven a bit by fashion. Ruby is sexy to young-ins because its virgin territory. Start-ups do this to attract other sexy young-ins that are full of energy.
Downvoted because your statements are completely false and based on nothing. If you actually used Rails then you will know better than to make such statement.
I've used Rails. (Goodness, I used Ruby in 2000. Get off my lawn.)
Plenty of the Internet's programming culture is driven by fashion. I saw plenty of projects written in Java in the early 2000s because that's "what investors want[ed]". When some of those Java programmers woke up from their XML-as-configuration comas in 2005 and 2006, they brought that sense of mission with them to Rails, ignoring the almost 20 years of dynamic languages getting things done up to that point. (No XML situps? Monkeypatching instead of Spring? Naked objects instead of beans? Auto-generated accessors? Ruby and Rails invented none of that, but good for Rails for attracting an audience.)
Ruby's a decent language, but it still suffers the growing pains of adolescence. It'll catch up. (A language test suite is a nice start.)
