Because heavy lift aircraft are perfect when you need to get something bulky somewhere else, fast. When it's multiple somethings and it's not time critical (da

Because heavy lift aircraft are perfect when you need to get something bulky somewhere else, fast. When it's multiple somethings and it's not time critical (days or weeks rather than hours), it's economically far more sensible to ship by sea. Sure, a service centre could really need half a dozen flights of engines, but given how well planned aircraft maintenance is, it would certainly be a turn up for the books to suddenly need such a number so urgently.