The best way to bootstrap language adoption is to get a big tech company to push it. Java (Sun, Oracle, Google Android), C# (Microsoft), JavaScript (all browser vendors, Facebook React), Rust (Mozilla/Microsoft), Swift (Apple), Go (Google).
Most of the popular languages are backed by one or more large tech companies. This gives managers the confidence to adopt them without reservation. It's the old "nobody ever got fired for choosing IBM" line, broadened.
Then there's python. Ruby (currently waning in popularity, but we are talking about bootstrapping popularity), php (well fb is a major company but php was popular long before that), perl, not to mention C and C++.
These languages have all at one point been "top" languages (moreso than swift, anyways).
Well, big tech backing is a sufficient condition for popularity, but not a necessary one. If you're looking for necessary conditions then that's a far more difficult question.
Why do other things (books, songs, movies, games) become popular? Some things just go viral for whatever reason and it's very difficult to explain why, even after the fact. Like trying to predict where lightning will strike next.
Big tech backing is no where near sufficient. Dart almost died (and the jury is still out). Facebook created a statically typed erlang, and I think that one is already dead, not a year after it was supposed to be announced
Most of the popular languages are backed by one or more large tech companies. This gives managers the confidence to adopt them without reservation. It's the old "nobody ever got fired for choosing IBM" line, broadened.