It doesn't matter how much Boise "wants to tag along". It doesn't make any sense for the AAC to bring in anyone else other than BYU.
Bringing in another two schools just so BYU can have a few closer football travel partners when it only impacts a couple of travel dates per year in a football schedule, doesn't justify the cost.
BYU is the ONLY school the AAC wants, therefore they have a standing invitation from the AAC as long as they want to come ALONE.