Suppose a supernova occurs in a star that initially had 10 solar masses. why would the likely end result not be a black hole?

When a supernova occurs, a very large portion of the stars' mass is lost. In order to create a black hole, at least 30 solar masses is needed, so starting with 10 and losing a large portion of that mass is nowhere near enough to create a black hole. The end result would be a Neutron star.