The availability of programmers who are proficient in a programming language is the single most important factor in programming language adoption. I think the continued popularity of C++ and Java has much to do with the fact; an enterprise wants to treat programmers as interchangeable screws, and a less widespread programming language would make this practice much more difficult. C++ was designed to be easier to learn by means of backward compatibility with C; This decision was good for programming language adoption; it was a good trade off, even at the expense of being a source of many issues with the language.
Interesting implication: I think that an enterprise with a less common programming language (like Scala or Rust), would have to treat its programmers much better than a competing shop that is using a commonly used platform like Java or C++; they have a greater investment in their workforce, due to the language/platform issue, are probably more likely to raise salaries every now and then and would be less likely to 'hire and fire'...
So adopting a less common programming language might have some non trivial implications on the culture and governance of an enterprise.
On the other hand there would be a lot of pressure to switch back to a more common programming language, in the event that the shop needs to grow significantly, these shops would then be inclined to port their systems back to a more common language...