[aczerepinski]

Speed to market. One person or a very small team can build a feature-rich app in Rails (or equivalent framework) faster than any other approach.

Plenty of companies end up building the wrong product altogether and need to pivot when they realize customers don't care about feature X and need feature Y instead. In cases like these you hope you get the right product out there and survive long enough to regret building with the fast framework instead of the finely tuned ultra performant version.