Two thoughts, Tourist...
1. Jet efflux passes under the THS at more than 60kts.... this will entrain more air all over the THS at a speed high enough for the deflected elevator to produce an upward force.
2.Without the deflection a mis-set or mis-calculated THS might produce an undesirable downward force.
3. If FCOM said "from 50 to 100 knots apply half forward side-stick" it might need an extra call when PM should be concentrating elsewhere, and plenty of us would forget! Simpler to do it from the start of T/O roll, which also avoids a change in rudder pedal deflection as PF applies full forward in a crosswind...