It's not a "just cuz" thing.
Internal provides fewer costs, and learning, and provides a safer transition with more stability. This can be perfect or cause a lack of growth in philosophy, culture, or new processes because it's more of the same that you currently have. It's conservative but stable. It works best when the position is more of a title than the actual job. This is Heupel's offense so no worries there. Clemson did this on offense and defense replacing their OC and DC. The safe hire also has downfalls, Dabo messed up IMO.
External hires can bring in new ideas, and unique experiences, and add to the culture, and a good hire brings in skill bump in multiple areas. The cons are, it's a wildcard. You always feel safer about the internal hire, but sometimes it's at the risk of a bad hire which requires good leadership to fix and that diverts efforts from other areas. It's considered riskier, nothing statistically backs it up that I know of, but without adding external hires, you don't evolve as quickly because you cannot train experiences.
You either didn't try or I recant my faith in you
