Forgive my ignorance, but wouldn't pulsar rotation decay over time, maybe millions of years? Shouldn't we expect to see many more slow pulsars since they could only slow down and never speed up?

but that is why these new objects are intriguing ... they look like they are giving off 'pulses' but live in the death valley, so they really shouldn't be giving off the type of emissions that we expect from pulsars (which need that fast rotation). So ... our models might be wrong! Or new physics!

great question! Yeah, young pulsars slow down over time, and eventually go into the 'death valley'. For pulsar emissions to happen they need to be spinning fast enough + have strong enough magnetic field. As these decay over time, then emissions turn off. Check this out: