The San Francisco 49ers are a relatively young football team. Between their three running backs, Jerick McKinnon is the senior citizen at 27-years old. Look at their other skill positions. Their two starting receivers will be a rookie and a player entering his second season. On the other side of the ball, the defense is predominantly young guys.
When you field a roster full of inexperienced players, particularly as backups, you get the results the 49ers did in 2018. It cannot be understated the value players get with stepping on the field, even if the season is already decided.