It's not even that it's popular among managers to move people around all the time. That's an awful framework for getting great work done.

People change jobs and you need to choose a language you can either easily hire for or train someone up in. Go fits the second requirement very well, and as more people learn it, starts hitting on the first. I introduced Go at two different companies to great success not because it's my favorite language (I would much prefer Rust, Haskell, Clojure, etc) but in reality, in my role as a leader of a tech org, hiring smart people and getting giving them the means to be productive as soon as possible for however long they want to work with us is key.