One of the biggest issues with bowl games is they don't take place during the season. It's complete nonsense to have a month or longer break between games. If a coach moves to a new school they have to go now, you can't really wait, you've got to work on recruiting and getting your staff hired. As a player when the transfer portal opens you need to enter immediately, if they wait too long there may not be as many opportunities available.
In today's world, the only postseason games that really matter are CFP games, we've seen the shift starting about 3 or 4 years ago, NFL prospects aren't waiting around even for major bowl games, neither are coaches on the way out, certainly not transfers. That's also the biggest reason the playoff needs to expand as soon as possible.