Do the places you are referring to not require heat? If so I don't see why having a separate heating and cooling system would be cheaper to maintain than a single system. Come to think of it I don't see why a heatpump would be more expensive to maintain than split AC. I guess there is some extra circuitry to make sure it doesn't ice up in the winter and maybe backup resistance heating builtin.

Most split A/Cs can also heat.

"Heat pump" can mean many things, from essentially "split A/C" (air-air heat pumps) to ground-source heat pumps, using floor heating for the output, warm water production from the heat pump, etc.