I mean there are fewer bowl slots than teams playing so not EVERYBODY. But if you're a P5 team and don't go like 0-10 or 1-9 you probably will go to a bowl game.
My guess is they start with the predetermined tie ins and go from there, and stick with an actual hierarchy as much as they can. For example, the SEC has not had enough bowl eligible teams to put anybody in the Birmingham Bowl recent years, my guess is that where you would see an SEC team with a losing record go. So you'll likely see something like a 3-7 Ole Miss in Birmingham or 2-8 Missouri in the St. Pete Bowl or something like that.