Step-by-step explanation:
There are only few supernovae that can be observed in our system. Class II supernovae formed due to explosion of large stars, that are found in most remote areas of the galaxy, may occur on a Milky way disk and are obscured by dust and gas.Now to see a pulsar, it is important to point to the radiation beam provided by the pulsar in our vision. So we will not be able to sense the pulsar, even though it occurs.
One other explanation is that the radiation strength from the pulsar decreases considerably with time (the magnetic field necessary for the development of radiation appears to decay rapidly). The pulsar eventually loses its brightness becomes more like a neutron star.