Because you're gonna eat the whole lobster yourself. You'd have to get a quorum of the other customers who are going to eat it.

You can if you go buy one from a farmer. In many rural places, you can then take it (or have it sent) to a butcher, and then pick up your coolers of fresh meat cuts to fill your deep freezer at home. I know people who do this, say once or twice a year. Better quality meat, often the animal had a better life on a local small farm, and per pound, far better price over the course of the year.

You absolutely can it's just logistically awkward. Just think about it, how often do you eat lobster versus how often you eat steak?

But I'm fairly sure that if you turned up at a farm you can actually do this, at least once or twice. Although long term I'm not sure it would be in the farmers interest because it's probably more hassle than it's worth.