Judd:
Cancelling reverse at 60 knots will cause the aircraft to increase speed momentarily because the engine RPM is still relatively high as it winds down towards 22% N!. In the simulator, prompt cancellation of full reverse (nominally around 88% N1) at 60 knots reveals the reverser lights extinguish by the time the N1 is passing 60% N1 on the way down to forward idle of 22% N1. 60% N1 forward thrust (however momentary) is a lot of power which is the last thing you need if runway length is limited.
That is because an incorrect technique is used. Reverse thrust should be reduced to IDLE reverse thrust until the engines are at IDLE thrust and then fully cancelled. Snap cancelling will achieve what you surmise. On LST's with cadets, during the mandatory RTO, it was a common thing to see at the 60kts call. They had not been taught properly and their eyes opened, especially when you explained WHY. Too much WHAT & not enough WHY in the teaching.