I believe it's purely marketing

Other languages (Java, C#, Go) are supported by massive corporate backers, who have vested interest in seeing them succeed. Erlang's own corporate owner tried to strangle it in the crib, and even since then they've been standoffishness towards anything apart from technical resources.

We didn't really see much marketing like material arise until things like Elixir came about, and even that is more following the ruby model, which is very dev oriented. And the world to which Elixir emerged in 2014 is very different than the world rails sprung into in 2004.

Devs can usually be convinced about how good BEAMlangs are, but without the glossy, you have a harder time convincing the MBA set