Subject: Why is only a small subset of all species of used for food?

With the great variety of plant and animals on this planet why do we only use 
such a small number of them for food?  Meat is only beef, pork, chicken, lamb, 
or fish and only a slightly larger selection from the plant kingdom.  The 
consumer can only buy what can be found in stores and stores can only stock 
what farmers will grow.  Isn’t there a large number of species left out that 
would provide good nutrition that could be raised for food?

Thanks.

Re: Why is only a small subset of all species of used for food?