What if .NET 5.0 replaces System.Collections.Generic.List to System.Collection.Generics.LinearList. .NET always owns the name List but they guarantee that IList is a contract. So IMHO we (atleast I) are not supposed to use someone's name (though it is .NET in this case) and get into trouble later.
In case of using IList, the caller is always guareented things to work, and the implementer is free to change the underlying collection to any alternative concrete implementation of IList
