Time-to-market with a viable product is extremely important. In the case of Rails in particular, the developer experience is such that even a very green program

Time-to-market with a viable product is extremely important. In the case of Rails in particular, the developer experience is such that even a very green programmer (for example, an entrepreneur who has taken a class or two) can bootstrap a working proof of concept quickly. That alone can be worth whatever drawbacks the language "speed" is, and is partly why Rails (and python stacks) were and continue to be popular. Also, language speed alone isn't a deciding factor if your bottlenecks are elsewhere: network latency, i/o etc. Having a "fast" language, for many projects, is something you worry about only after achieve some kind of success, and that success is made more achievable by having good developer tools.