Tactically, it may very well be the case that you do not need to spend much time in Kingsport.
However, compare that to the other two 'big board' expansions.
Dunwich Horror: Gates will open here very often. Monsters can feed Vortex and awaken the Horror and also feed the terror level. If Dunwich horror wakes up, you need to go there and kill it to keep Doom Track from accellerating because every time the horror moves, you add a doom token. Killing the Horror is a fun challenge. Sealing a gate in Dunwich will add to the victory conditions of the game.
Innsmouth Horror: Gates open here very often. Monsters will feed vortex and cause a Deep One uprising and awaken the GOO immediately as well as feeding the terror level. You need to spend clue tokens to get the feds to raid the place. There is also the added challenge / risks from Marshal Law and having to draw Innsmouth Look cards. If you go out to the reef, you need help to get back. You go to Innsmouth both because it is needed and because it is fun. Sealing a gate in Innsmouth will add to the victory conditions of the game.
Kingsport Horror: Gates never open here. If a rift opens, it open where the gate opened. No monsters show up in Kingsport except monsters with special movement rules. Rifts will accellerate the doom track so there is a reason to go out here. You can also try to get 'Changed' or 'Captain of White Ship'. This will require monster or gate tokens, neither of which you are likley to get in Kingsport. And getting the 'Changed' state will take up yet more time (at least 3 turns). However, time spent in Kingsport cannot advance progress towards winning the game. it might help, but most likely it will be time spent not sealing gates. At best, your just buying time to keep the doom track and monster population under control.
Kingsport takes up just as much table space as Dunwich or Innsmouth while adding a whole lot less fun. It is not a bad expansion, but out of the 3 'big box' expansions, it is arguably the weakest.
I just cannot see how arguing 'Kingsport might not be interesting to explore, but at least you do not have to spend much time in Kingsport' is a good selling point. The entire location is just a timesink with minimal incentives to visit. Innsmouth kind of sucks to visit with the crazy number of chances to get devoured or arrested, but it is interesting and you are given reasons to be there. it adds more strategic choices to manage. Dunwich is not nearly as brutal but there are positive incentives to kiling that monster. And after dealing with a Deep One Uprising or killing the Dunwich Horror, you do not have to spend 2 or 3 turns going somewhere else to get back to the business of sealing gates.
Kingsport can be improved.