[elihu]

It kind of sounds like they're running into some limitations of GHC: it tends to take a long time to compile stuff, and it tends to generate some very big binaries. For most applications, those aren't major problems but in their use case (hundreds of thousands of lines of code deployed to many servers) it is an issue so they're working around it. That allows them to keep working in the language they prefer and are productive in, which is great.

Improving GHC compile times and reducing the binary size would be better, but presumably a lot of work has already gone into those problems and if it were easy someone would have done it by now. As for myself, I really like using Haskell and I'm glad whenever I hear about it being used in industry.