The climb tq limit is something that has only been introduced in the last 8 years and it seems a lot of old courses still don't teach anything about it and some instructors/check and trainers still choose to ignore it.
This is my educated guess but purely that as I am open to be corrected. The climb tq limit is there to keep you under max itt and Ng. This is the same reason as Takeoff Tq limits all they are there for is to give the pilot a Tq setting that will keep your ITT within limits.
This makes it simpler for a pilot to have a figure to set instead of taking a best guess.
But as I say I stand to be corrected!
I am impressed you are actually reading the book and looking for answers there are too many people who just don't bother these days!