I was of the understanding that CLT was tacked onto the end of the BWI because all the 767s that operated both routes were moved to LHR. One of the Bermuda agreements prevents BA operating direct from LHR to CLT so it had to become a shuttle.
I, for one, shall miss the BWI-CLT shuttle. It always made for (ahem) interesting flying and it also meant that we got an extra day (or half day) in Baltimore. C'est la vie.