I've had 3 games this spring so far. Only 1 ran the full time.
In one, the score was 40-0 at half time. No mercy rule in that league, but the coaches can come together and change the time to play - they halved the clock for the 3rd and 4th quarters. Winner was obvious.
Game this weekend - right after 2 minute warning score 21-6, the winning team's QB gets taken down hard. We are delaying for the medics.
The coaches both come out and say - the game is decided, lets just call it now. The loosing coach is well known for being super aggressive and pushing hard. I was really surprised that the offer came from him.
The R debated having a few kneel-downs at the other end of the field, but decided to just call it that the time had run out.
I think maybe a difference here is that it is not 4 years and you are finished forever like most high-school players, but they can reasonably play for 10-15 years if they stay engaged and enjoy it.