I think the reason most recurves don' t have leather covers on the handle is because it would be harder to fit one to the molded handle than it would be with a straight stickbow.

I don' t know that there is a practical reason for a leather grip other than maybe leaving some place for the dirt from your hand to accumulate. I' ve noticed no accumulations on the wood finish of bows without the leather, so perhaps that' s not a practical reason either.

I had one flatbow that was so badly tillered it would actually blister the bow hand unless the grip was soft, smooth leather. That was before I realized the problem was the tiller. It might be too that leather has been used on bows that kicked, somewhat mitigating the annoyance, but who knows really?

My Asiatic bow is leather covered because it is leather covered, all over except for the Sihas. It doesn' t really matter though because I use a glove on the bow hand to protect my knuckle from the fletching quills.

Probably leather-covered versus bare handles is practically irrelevant in most cases. With wood bows, there' s little chance one' s hand will stick to the bow in cold weather and if the bow' s too hot handle, it' s probably going to come apart pretty quick if it hasn' t already. So I guess it would be mostly an appearance issue and nothing more.