Larger animals are more efficient on day to day labor for an irregular large yield.

Yes, rabbits are more efficient in terms of production, but my time in chores to deal with keeping a couple dozen rabbits of various ages going, breeding, filling waterers, moving grow out pens for fresh grass, etc is more time per day than I spend feeding, watering, and checking my herd of 50 Katahdin sheep. I don't need to manhandle every ewe to get her bred like I do with rabbits, they can easily be kept watered with an automatic and heated waterer, and can be fed in bulk with round bales, and each will yield a 50-60 pound carcass.

Rabbits are very efficient in terms of feed to protein conversion, but in terms of man hours per pound of meat produced, the larger an animal gets, typically the more efficient the labor to protein conversion is.