Parameterized packages are interesting but they come with their own problems. It can get tedious if I want to use, e.g., a stack with multiple different types. They also lose some of the flexibility that comes with scoping type parameters to any function/method/data structure.
On the other hand writing such packages becomes easier as only two syntax extensions are needed (package header and import). You can easily abstract a package by replacing a concrete type with a package level parameter. More importantly, there is no other mechanism to tie together a bunch of objects, functions, methods etc. to the same parameter types.
