You currently can bend C++ into ways to have such a type system. The usability this introduced through additional complexity is just very very bad. So no one does it because bad usability means bad productivity and getting a project done with bugs is often better then getting it not done at all (sure there are exceptions!).

There is the saying that once you got a Haskell program to compile, it usually just works, and I personally found it to be true a lot. But getting it through the compiler can indeed be much more of a journey than in, say, C. And I realize that the work you have to put in to just even being able to run something can be discouraging, maybe going against a natural (or maybe just common) affinity towards tight, iterative "change-compile-try" approaches.

Still, in cases where it really matters, i.e. system software or common, but often mission-critical software like sqlite, maybe it's worth taking the jump?