why doesn’t my terp slurper spin the pearls around?

This could be many reasons.  If you do not have an Elev8 Terp Slurper or some other good brand, the holes may not be at an angle to allow the spin.

Another reason could be that your terp slurper is dirty?  If this is the case, the oils get thick and can hold the pearls in place, not allowing them to move.