I might sound bitter but after about 3.5 years with Elixir my answer is very simple and boils down to:

Habit, confirmation bias, sunk cost fallacy.

Namely: people have gotten a lot of battle scars by working with what pays their bills -- PHP, Ruby, Python, C#, Java -- and they refuse to look at an alternative because that would render their huge time and energy investment moot (in their eyes at least; I don't see why this has to be the case but plenty of people have been adamant about this without giving an explanation).

I've only become a better programmer since I adopted Elixir but I never stopped using other languages.

All of that plus what PG calls "the middlebrow dismissal" are the main reasons IMO. People are just too set in their ways.

I've got those scars but I still find erlang refreshing when working with it. Unfortunately, as software engineers, we work in groups and there are many people having these scars. However, the erlang experience changes one forever.

As you said, unfortunately programming turned out to be quite the tribalistic activity indeed.

I got severely disheartened that 2-3 casual mentions of Elixir were enough for several people in this thread to attack and quickly stereotype me. I think I'll just keep quiet, or at least not mention what I work with. This seems to get the message across much better.