Presumably, the answer is that the beam doesn't usually find us. Remember, the reason we discovered pulsars to begin with is that we observed the periodic behavior caused by the beam hitting us. If there are a ton of pulsars that don't hit us (and I'm guessing that there are), it seems like it would be very challenging to identify them as pulsars and not some other celestial object.
It's also possible that, angular momentum being what it is, that pulsars are biased towards rotating in the same plane as whatever galaxy it resides in, in which case you'd be more likely to hit a planet than you would given unbiased random chance.