Also: many libraries have little or no use for generics, and even if it's some benefit it's still worth asking if it's enough benefit for the added complexity (e.g. replacing "any" with generics is probably good; replacing "string" or "int" with generics: not always).

Also also: in quite a few cases switching to generics is a backwards-incompatible change or an "ugly" change (similar to Foo() and FooContext()), which makes adding them to existing libraries a bit painful.