I think because it's easier to learn and require less code so startup may focus on product instead of code. This should be true especially if you compare RoR to

I think because it's easier to learn and require less code so startup may focus on product instead of code. This should be true especially if you compare RoR to java technologies, but i'm working on a project where Grails was the requirement and i think Grails has a good future because thank to Groovy it requires a lot less code but has its foundation on java frameworks (hidden to the developer) which are very stable, solid and mature (and obviously complex!)