Because the guarantees are largely exaggerated, require you to use specific language extensions (that you have to find out about somehow), and are often present

Because the guarantees are largely exaggerated, require you to use specific language extensions (that you have to find out about somehow), and are often presented in a largely esoteric manner. Yes, you can write some advanced type-fu to provide interesting guarantees on the type level. But by the time you've learned how to do that, your colleagues will have delivered multiple projects in most other languages with test suites that provide similar guarantees.