Google Maps boundaries aren’t the most accurate. You can look up property records for KCMO and see it’s almost entirely inside KCMO (though it does span multiple parcels).
What’s more interesting is that while the building is in KCMO, the address of the gas pump canopy is in KCK. I’m sure they all just use the address of the entire business in KCMO for all legal purposes.
It’s because they’re bigoted.