It makes changing and tweaking an adventure school a very long and drawn out process.
Sometimes you even want the changes because you've switched from solo to group hunting.

Is there any reason why this system is needed?

For a total pool of 1200 TPs, you get a max of 300 BBP you can use at any one time.

Not sure how long it takes to build the stock of BBPs up again, but we're talking about a week to make a complete TP re-allocation... if you make daily adjustments as your BBP stock builds back up.

Possible choices could be:

Pay a trainer for those BBP to come back (like visiting the TP trainers that used to be in the gatehouse in Tazoon)
Increase the rate BBP accumulate
Get rid of the BBP system altogether and allocate TPs as you like, when you like.