1. More popular languages you can find less expensive developers for...(or more total developer talent for a given amount of money)
Which isn't necessarily a good thing. There's a huge difference between good and bad programmers, and the more popular 'x' is, the greater opportunity for the signal to drown in the noise. Relatively fewer good applicants.
I've for instance heard that one reason Standard Chartered Bank is happy with their Haskell usage is that the quality of the applicants is so high. There's not a lot of weed to sift through. And I'm not surprised given who learns and uses Haskell.
4. More popular languages tend to be faster. Usually a shit ton faster. Java has gone from a bloated mess to a bloated mess that is often within spitting distance of C on performance shootouts. That's from the popularity spurring further development. C is almost always king of the hill and nothing is faster. Python? Rust? Whatever n00bs. Those languages may be nice to write complex code that only gets run occasionally but if you need high end performance they aren't going to cut it.
Micro benchmarks usually doesn't tell you that much about what the efficiency of a large application is going to be. Case in point, at Ericsson we routinely beat the performance of C/C++ on large scale projects with our own Erlang, even though Erlang didn't even have a compiler and was left in the dust on micro benchmarks. But as it fit the problem so much better it in practice became an issue of "doing the right thing somewhat slower" rather than "doing the wrong thing blazingly fast".
However, for the limited tasks where languages like 'C' shine, i.e. device drivers and similar low level task, i.e. limited in scope, well defined, and making the most out of specialised hardware (specialised hardware beats 'C' on a general purpose CPU every day of the week), there's no need to go to another language than 'C', as it's already there, the most mature, and well known. So, we'd use a combination of Erlang and C. It's not an either-or proposition. Trying to write the whole thing i Java, because it's "almost as fast as C" would be a complete exercise in futility...