Why aren't classes like BindingList or ObservableCollection thread-safe?

Question

Time and time again I find myself having to write thread-safe versions of BindingList and ObservableCollection because, when bound to UI, these controls cannot be changed from m

Answer 1

To add a little to Jared's excellent answer: thread safety does not come for free. Many (most?) collections are only used within a single thread. Why should those collections have performance or functionality penalties to cope with the multi-threaded case?