Ohh medevac you seem so young and keen ( i like that )
Having been an all sides before group, brigade management and the best place firefighter. You should have been told why you are not getting the PBI. Sounds like it is not geeting back from group/brigade management to you.
At group the decision would have been made by the GO and brigade reps, they might have had some good reasons( i don't know the facts) but it could be as simples as a budget issue ( hey don't all jump up and down over this, money makes too many decisions )if your group has X amount of PBI to clean each year and budgets are tight, where is the money coming from, what do you cut back on
Ask at your next brigade meeting why, it is your right to question or just go and ask your captain or if you see your GO just ask him why. The easiest think is to sit back and have a go at the system, sometimes you win if you question