DL has no reason to add something like CLE-CVG when time-efficient connections are available CLE-DTW/JFK/ATL-CDG.

If 'Start your TATL journey with a 2-hour drive' is the best the PIT airport authority can come up with for CLE-origin passengers, they should know a 2:15 drive could get passengers to DTW for non-stops to LHR/AMS/CDG/FRA and seasonal FCO.