FWIW, here is an excellent article from the AJC yesterday describing how GT fell to the Quick Lane Bowl.
https://www.ajc.com/sports/college/how-georgia-tech-fell-the-quick-lane-bowl/j8F3RzX2rl8zj1K7Eu2F4I/
Ultimately it comes down to ticket sales. GT is hurt in the Bowl Execs eyes by having at least 3 straight bowl games where it did not sell out its allotment, by the idea that college football teams in big cities don't travel.
Getting a tier 1 bowl was always going to be something of a pipe dream. ACC has 4 tier one bowls. By ACC rule the ACC Championship game loser cannot fall out of the Tier 1 bowls (so Pitt ends up in Sun). NCST and Syracuse having 9 wins have to be taken next ahead of all the 7-5 teams. That left only 1 slot left in a tier 1 bowl, that being Belk. Belk has never taken a non Top 25 ACC team that is not from the Carolinas or Virginia. Even losing 3 of their last 4 games Belk felt UVA was likely to sell more tickets than GT.
So GT was going to a tier 2 bowl. The Military Bowl chairman says in the article that while it would have been great to have Johnson for his final game, that ultimately it comes down to who they think will sell the most tickets and based on how quickly VT fans have been purchasing tickets they made the correct decision.
if you want GT to go to better bowls you have to go to bowl games and you have to buy the tickets through GT.