Many people don't really understand the languages they learn until well after they are done mastering them. And some never really pick the deep detail there is

Many people don't really understand the languages they learn until well after they are done mastering them. And some never really pick the deep detail there is to semantics and type theory. If it is done right, the language might feel nice to use or elegant but users might not articulate why that is. That can be a key selling point. And of course there are a lot of languages where the type system was a bit of an afterthought that got popular anyway. Javascript and other dynamically typed languages comes to mind. Rust kind of sits on the other end of the spectrum. And it has a deserved reputation for being a bit hard to learn because of it.