For one, there might be trade-offs against dimensions other than safety and expressiveness. Performance, corporate support, libraries, popularity, learning curves, similarity to other languages...
For two, popularity is simply not strong correlated to quality. Popularity is a social function driven by, well, social factors. It's heavily path-dependent and noisy. There is absolutely no guarantee, not even close, that the "best" thing in any sense will be the most popular, or popular at all.
Clearly there's a trade off or else everyone would just use Haskell.