I use rails because it makes thousands of good choices that I never have to make. If build apps the rails way I don't have to deal with a mountain of tech debt (in the form bad or ever changing choices).
I think most people that dismiss BEAM right off the bat either don’t understand the built-in beam process/supervisor/etc. model with its inherent fault tolerance, etc, or assume its not useful because it doesn’t address their use cases.
That or it’s a evangelist from the church of AI speaking based on faith rather than reason.