Another consideration is that a yacht engineer must typically be cabable of performing all of the usual engineering duties, then change his hat and step out to charm, entertain and look presentable to the guests, be they owners or charter guests. Then, once the dog and pony show is over, except on the biggest boats, be willing to pitch in and help elsewhere on the boat, either standing a deck watch, helping in a washdown, or who knows what else.
All this, coupled with solid engineering skills makes good yacht engineers a relatively rare bird.
Consider too, that the engineer on many if not most yachts also performs engineering duties on his own. No team of mates and oilers to do the nasty work.
Oh, and the grass always looks greener on the other side. My brother is a merchant mariner and, while he thinks yachting looks pretty cush, I wouldn't mind his workday or four months per year off!