3. Atlanta doesn't fully trust Penix
Michael Penix Jr. looked the part of a franchise quarterback in the team's final three games. You saw clutch ability and continual growth in a very short window. Penix has given the team every reason to believe he can be a starter and help be a part of the solution for the Falcons.
This is the same front office that paid top dollar for Kirk Cousins and weeks later drafted Michael Penix Jr. It was a move that never made sense showing a lack of faith in both Cousins and Penix. Now the Falcons are stuck with a massive contract for a quarterback they are attempting to use as the primary backup.
Either this is posturing on Atlanta's part, or the team still doesn't fully trust their young starter. Cousins is great insurance if you don't trust Penix's health or consistent production. Even if they believe in Penix's talent, the quarterback does have an extensive injury history. One that could concern the team enough to attempt to keep Kirk Cousins as the second option.
This is the most logical reasoning behind keeping Kirk Cousins if it isn't the posturing it appears. Penix is unproven and has an injury history that suggests the need of having a reliable second option. If healthy, there isn't a backup in the league better than Cousins.