Here's (somewhat) of an explanation of how the venue's are chosen for each team.
"In talking to (executive director of the College Football Playoff)
Bill Hancock, what Bill told me is that the selection committee will advantage the number one team and their fans without disadvantaging them," Peach Bowl, Inc. CEO & President
Gary Stokan said.
So, advantaging a team without disadvantaging them?
"That may sound like an oxymoron but It's meant to say, okay, Ohio State, if they're number one, in this case, we would want to put them in a place that geographically is good for their fans to get there and advantages their team and their fans," Stokan said.
Stokan would go on with a hypothetical where the Buckeyes take care of their business, end up as the top-ranked team and the selection process takes special consideration for Ohio State under these parameters.
"Let's say (they were to face) Georgia," Stokan said. "Now, wouldn't want to put them in Atlanta. So, they would take that matchup, in Atlanta (Georgia), if the season was over Ohio State and Georgia and move it out to Phoenix."
https://ohiostate.rivals.com/news/no-1-in-cfp-to-be-advantaged-without-being-disadvantaged-