Why are pulsars not always associated with supernova remnants?

It is commonly acknowledged that pulsars are rapidly spinning neutron stars with strong magnetic fields.

When a star ages, fusion reactions create heavier and heavier elements until the core is mostly iron. Further fusion reactions are not possible because fusion reactions involving elements iron and heavier consume energy rather than release it. This is how neutron stars are formed in the late stages of stars over 8 solar masses.

After fusion reactions cease, the core of the star collapses due to gravity, heats up, and forms a neutron star. The radiation released during this process destroys the remaining portion of the star, resulting in a Type II supernova.

Therefore, it is thought that all pulsars and neutron stars are related to supernova explosions.

While many pulsars are found inside supernova remnants, or nebulae, some are not because they have drifted away from their formation site over time and are no longer inside the nebula. This is because, during the formation of the neutron star, the object must gain angular momentum in order to become a pulsar. It can also gain linear momentum.

Other than supernovae, pulsars can also form as a result of binary star systems or the collapse of massive stars that do not produce a visible supernova explosion.