Beam geometry: The radio emission from pulsars is highly beamed, meaning that it is emitted in a narrow cone-shaped region. If our line of sight to the neutron star does not intersect with the beam, we will not detect any pulsations.
Emission mechanism: The exact mechanism that produces the radio emission in pulsars is not fully understood, but it is thought to be related to the rotation of the neutron star and the presence of a strong magnetic field. Some neutron stars may have magnetic fields that are not strong enough or aligned in the right way to produce detectable radio emission.
Observational limitations: The detectability of pulsars also depends on our observational capabilities. Pulsars can be faint and difficult to detect, especially if they are located at great distances or in regions with high levels of interstellar gas and dust. Observational biases can also affect the number of pulsars that are detected.
Therefore, while many neutron stars are observed as pulsars, there are also a significant number of neutron stars that remain undetected or have not yet been identified as pulsars.
