In what cases might the TTO opt not to patent an invention?
An invention might be useful, novel and non-obvious and still not repay the expense of filing and prosecuting the application to the point of issuance. Primary consideration is given to the commercial utility of the invention, the competitive arena, the existence of prior art, the stage of development of the invention, and especially interest by potential licensees. If those components are not there, then the TTO might opt not to patent the invention.