Most of the benefit of types goes away unless _everything_ is typed... my libraries, the libraries my libraries use, etc. I should be able to jump around in and out of library code following types and usages thereof in my IDE, making conclusions that are accurate based on what the types say.
When some of your libraries (or indirect dependencies) don't have types, you can no longer ever make any firm conclusions when exploring a complex codebase based on types. I want to change a method in the Widget type, and my IDE says it's used in 4 places. But in reality, that just means 4 or more places, who knows if there are others.
Adding types to a language that doesn't already have them is very hard for this reason. Until many years pass and they're in universal use, they add little value.