With corches there is the human factor and there are many who are risk averse than actually trying to make things happen (why you had guys who had 3 yards and cloud of dust mindset, prevent defense, etc). They would rather go with the known than unknown then you add the ego of wanting to be smartest in room and not being questioned in interviews about their choices. Sometimes they just love a kid more or the more talented kid they want to "teach him a lesson" (derrick smith situation)
Sometimes they see themselves in a more limited kid and want to give him more opportunities (randy back in day with glenn cook). Some corches will put a guy who is extremely limited on field because he is a hard worker (this is still shayon green's team) but cant make plays.
Its alot of different reason but people think it changes but it doesnt, it happens from every level, from pop warner to the highest of levels
with Scott he had seniority, experience, knew the plays and had the heart string story of many injuries but a hard worker. It wasnt until he started being knucklehead and getting bonehead penalties and our corches getting questioned in media for weeks straight did they make a change. Mind you everyone knew what Greg was as a true freshman in practice and RAVED about him from first practice
