Domestic US ... yea, I can understand that might not be profitable. I'm surprised nothing happened with the Silver Caribbean network (which has also changed hands like 10x).
Breeze also flies TPA-EYW, although not nearly as many flights as Silver.
Hm .. what destination can United add that boards at the exact same time as IAD, EWR, DEN, IAH, and ORD to further maximize confusion at the crowded gates? I love my United, but boarding in Tampa can be chaotic.
They can take a page from American and add another hub flight like EWR less than an hour from the other one with a similar flight number and giggle from around the corner.