Well, it kind of makes sense to mount it right on top of the engine.
That saves on running all the sensor wires from their locations on the engines all the way to either the left or the right fender well, and then back.

There probably is one nice, simple set of wires that run from the firewall to the ECU, and that's just about all you need to pull in order to pull the engine out, and swap in a new one, aside from fuel and coolant lines, of course.

BC.