I've noticed this frequently in the NFL. When there's a kickoff that is downed in the end zone for a touchback (or is out of the back of the endzone), the coverage team still runs all the way down the field. Sometimes the receiving team is already walking off the field as the referees take the ball to the 20 yard line and still the coverage team is running full speed and they don't stop until they reach the end zone. (At which point they have to turn around and run back to their bench). Is this a macho thing? Intimidation? Young players trying to show their dedication and hustle to the coaches?
From personal experience (high school and not the NFL), we were required to run through the goal line every time.
There are a couple of reasons I could see for them doing so:
If the kick does not go out of the end zone, the player may return it. There are plenty of players that will return a kick from 8 or 9 yards in the end zone if they see an opening. If the players slow down and the returner takes it out of the end zone it could be a big return.
Players are on a full sprint for 40+ yards sometimes and instead of breaking down, they choose to contine through the goal line to slow down at a decreased rate (possibly limiting a muscle pull injury).
Players on special teams are often the last players on the 53 man roster and do not want to give off an impression that they are slacking or taking it easy. Especially if they are on the team for only kicks and punts. It may have started at some point and players decided they wouldn't be the guy that didn't sprint down to the goal line.
Special teams coaches may require it.
I cannot say for certain the reason other than I am sure they have a good reason for it. Whether it is keeping their job or for strategic purposes.
I always coached my guys to run through the end zone at full speed for the following reasons:
- Why not? It is a free sprint that keeps them in shape for the next kickoff.
- Most importantly... Intimidation. I want the returner to see how hard my guys are working and decide to kneel when the ball goes 2 yards deep in the endzone.
Why do they do it? Because I told them too and they won't be on kickoff if they don't (and possibly the team).