Most residential units match one outside compressor to a single interior evaporator because to use one exterior unit for both you'd need way more complex valves

Most residential units match one outside compressor to a single interior evaporator because to use one exterior unit for both you'd need way more complex valves to control which unit is receiving cooling. Even if your matching one to one you have the added cost of running all the lines associated with that including having a trades person coming out to install and charge the extra piping between the two units and installing the exterior unit that will need power. It's just massively simpler to have a complete unit you can drop down and optionally connect to water.