bluGill answered this well. To add a little: the total load of all but the smallest systems (9/12k BTUs/hour) is too large for a typical 15A @ 120V circuit, so most outdoor units need 220V. That means a new circuit. Also, building code in the US typically requires a shut-off box right next to the outdoor unit.
At least in the US, many systems power the indoor unit(s) from the outdoor unit. My guess is that since a control wire is required anyway (for central control of fan speed and direction), the manufacturers think it’s easier to power everything from one run.
At least in the US, many systems power the indoor unit(s) from the outdoor unit. My guess is that since a control wire is required anyway (for central control of fan speed and direction), the manufacturers think it’s easier to power everything from one run.