at many/most airports the operations have been combined, however as you noted there are still some separate operations. This is partially due to restrictions at the various airports, such as lease restrictions or the lack of avialable space to combine operations. UA does not have the power to move other airlines, it needs to work with airport operations and in some cases this can be slow.

a fairly complete list (ICT is not listed) of the "problem" airports can be found in "Confirming the correct terminal for your flight"