Why is contract design not more popular?

Question

In theory, this seems like a great solution to avoid mistakes, but why in practice do we hear so little about it?

Why can't we support it in Java or .NET anymore?

Answer 1

I also searched for this answer. But it does not seem to be popular among the programming world. Therefore, not many people discuss this. I tried to use it, however I consider it a hassel to really think which contracts I should write while I program. However, this is good for debugging.

You tried? What do you think about it?