Final answer:
Pulsars outlive their supernova remnants, and some receive a 'birth kick' that propels them out of the remnants. Orientation of pulsar beams in the three-dimensional space also affects our ability to detect them, as many beams do not intersect with Earth.
Step-by-step explanation:
The reason why all pulsars are not located in supernova remnants is multifaceted. Firstly, the lifetime of a pulsar is significantly longer than the time it takes for the visible gas of a supernova remnant to dissipate into space, meaning many pulsars outlive the remnants that birthed them. Additionally, during a supernova explosion, some pulsars are given a birth kick, resulting in the pulsar being ejected from the remnant and moving away at high speeds, leaving no trace of the origin.
Furthermore, due to the three-dimensional nature of space, many pulsars' beams do not intersect with Earth, rendering these neutron stars invisible to us. Thus, the visibility of pulsars is limited by their beam orientation relative to Earth, and we miss many because their beams sweep over a circle in space that does not include our planet. This spatial relation emphasizes that while pulsars are a leftover product of supernovae, their detectability is influenced by multiple factors beyond just their progenitor's remnants.