Jordan Love vs Ian Book

Veteran players giving pointers (which is not really tutoring) to rookie players on the sideline is great, but it is the coaches who are getting paid to develop the players; that is literally their job; it is not the starter QB's responsibility to make sure the backup QB is ready to play should he get hurt, it is the coaches' and the backup QB's responsibility to make sure the backup QB is ready, and getting pointers from the starter on the sideline is not going to cut it.
He's been there for years. There's been way more opportunities than just sideline time.

This happens on regular jobs as well. They hire someone and ask other employees to let the new person shadow them to learn. Now, as a teammate you can choose to just let them watch you in action or you can let them watch you and then spend time teaching them as well. Great teammates will go the extra mile.