check airman
I would hazard a guess that the much smaller total thrust increment on the AE engine between idle and full power maybe a factor, a smaller fan will be easier to spin up.
I once flew a 737 which seemed to have quite a high taxi speed (but we had several different variants 300,400,500) after 3 sectors i discovered that the ground idle CB had been inadvertently pulled by the F/0 seat belt shoulder reel strap, learnt something from that !!