A4 has described the easyJet SOPs exactly. It's worth noting however that there is no restriction on using REV idle all the way down to stop:
FCOM LIM-70 P 3/4:
‐ It is not permitted to select reverse thrust in flight
‐ It is not permitted to back up the aircraft with reverse thrust
‐ Maximum reverse should not be used below 70 kt. (
Idle reverse is permitted down to aircraft stop).
My only point is that there's no need to ride someone, get on their back or even
yourself if they forget, leave it to 10 kts or take their time.
As for why someone would leave it to the taxiway they're either one of these 'I won't be rushed' types that take it overly slow, it was a high speed turn off on one vacate and a 90 degree turn off on the next or they simply forgot until reminded by PNF.