Are self maintained language frameworks worth it?

I recently joined a company that uses Haskell for its backend. On top of that, they’ve built their own custom framework for it.

Since I’m new to both Haskell and this in-house setup, I’ve been wondering:

• Was it really necessary to build a whole new framework?
• What kind of circumstances make maintaining your own framework worthwhile?
• Are the trade-offs—like developer ramp-up time and maintainability—justified in the long run?

Curious to hear your experiences or opinions—especially if you’ve worked with in-house frameworks in lesser-used languages.