It is to do with the Vm speeds; so I was instructed years ago. Further, the performance calculations have a little buffer between 100% perfect and the line duffer on the day. Thus they say it is not necessary to increase thrust to achieve the profile.
What I find disconcerting, and another dumb don in knowledge, is that people say it is not allowed to increase thrust. Some say they are nervous that once PF has the correct rudder inputed close to the ground it would be disturbing to cause an adjustment.
Personally, IMHO, there should be a 'note to self' in the training and during the manoeuvre: "choose 1.......a/c is performing as required......leave thrust alone. A/C is not climbing as required.......increase thrust and control a/c."
To not teach people the pro's & con's of use of thrust is negligent, but I see it every day.