Why not always use Generics?

Question

I am reading existing posts on Generics at SO. If Generics has so many advantages like Type safety, no overhead of boxing/unboxing and it is fast, why not always use it? Why

Answer 1

Sometimes "object" collections are simply unavoidable. Often this happens when there's multiple types in the same control/collection - the only type they have in common is "object", and so that's the best type for your collection.

Another case for object (non collection related) that pops up from time to time can be seen with the PropertyGrid. A third party property grid may allow you to attach a "validator" which returns whether the users new value for a given property on the grid is acceptable. As the PropertyGrid does not know what properties it will be displaying, the best it can give the validator is an object - even though the validator knows exactly what type it will be called with.

But as per Mark's answer - most (all?) of the non generic collections in .NET are only there for legacy reasons. If .NET was remade today you can be sure the standard library would look very different.