The staff kept EVERY STIFF KNOWN TO MAN in the games....
Highsmith can't possibly have better upside than Jamal Carter.
Only rationalization is that the coaches put a premium on guys knowing their assignments.
It's basically a zero sum game.. Play the more experienced less talented player who will know his assignments and therefore be in the right position to make plays.
Or play the more talent less experience who's physical talent and skills will make up for being out of position.
At the end of the game, the less talented but more experienced player will make plays and tackles by virtue of being in position but will also miss some tackles and not make plays because of his limitations.
On the flip side, the more talented but less experienced player would also make plays and tackles by virtue of his physical abilities but will give up big plays due to being out of position.
So Golden probably believes there is not an immediate net positive for playing a guy like Carter over a guy like Highsmith.
And given that AL Golden is big on rewarding kids to buy into his system and are good soldiers like this SENIOR class that stuck around was it's easy to see why he chose to go with them over the more talented younger players.