Say you own a great, big sandbox. Say your great, big sandbox is the neighborhood hot spot, where all the kids come to play. Say your sandbox is such a big deal you even have people selling lemonade and cookies to the kids and their parents.
Then, say one of the popular kids makes some sort of disparaging, off-hand remark about your sandbox, the kind of remark that might make people quit coming to play, thus putting your lemonade and cookie vendors out of work.
What do you do?
At the worst, you kick his butt out of the sandbox with orders not to come back, and at the very least, you make it clear to him that if he's going to play in your sandbox, he's going to keep his mouth in check.
In fining Sprint Cup competitors Denny Hamlin and Ryan Newman, that is what NASCAR has done. They have made it clear that the sport's hotshot and the former Daytona 500 champion are free to play in the sandbox with all the other kids, but they better not say something that will damage the image of the sandbox and hurt those lemonade and cookie folks.
NASCAR has been vilified for having the audacity to reprimand two star drivers who dared to speak their mind and for playing big brother while looking out only for their interests. In reality, especially in the case of Hamlin, NASCAR's actions have protected not only their interests but the interests of everyone else who plays in their sandbox, from the other drivers to the people who sell merchandise at the track to the people that pick up trash when the race weekend is over.
As a superstar, Hamlin is responsible for more than just representing his #11 race team, his fans, FedEx, and his other sponsors. His standing in the sport is such that his actions and more-so his words affect everyone in the sandbox and have the gravity to potentially do damage to NASCAR racing. People will cling to such controversial and possibly damaging statements as his outright claims of phantom debris cautions, whether legitimate or not.
If NASCAR's credibility is damaged, then the effects stretch well past the sport's brass. The ripple effect reaches through the garage area and grandstands and out into Souvineer Row and along the way touches everyone with interest in NASCAR's success, including those who inflict said damage.
Thus, in order to protect not only its own image but also to protect those in its sandbox, NASCAR had to and did act accordingly.
It is their party, after all, and they'll do whatever they need to in order to keep it rocking.