if sheep have four legs, how is it you only get to legs of lamb,?

The digit 2 is spelled two!

The front legs do not have much meat. The rear limbs are a lot meatier. You see the same with pork. The ham is the thigh muscles of the rear leg, but the front legs are rarely available for retail sale in this country because there is very little meat. The front limbs of pigs are a delicacy in some Asian countries. It is the same for most other 4 legged animals. Frogs, salamanders, lizards, crocodiles, dinosaurs, birds and mammals generally have more massive muscles on their rear limbs than their front limbs. The bird wings and drumlet are a lot less meaty than the thigh and drumstick. I reckon 4 legged animals most often have rear wheel drive instead of front wheel drive.

They have four legs, but they have two pairs of DIFFERENT legs.

just like humans, the rear legs of four-legged animals are strong and meaty, while the font legs are thin and bony

Only the rear legs are used for 'leg of lamb'. The front ones are thinner. The rear legs have those nice thighs.

You only ordered 2 legs duhhhb

Because the front are hands.