What do you think of the recognition every year of a tragedy that has been in the public eye?

I don’t understand the necessity of the yearly recognition of tragedies that have happened. For example, the yearly recognition of the 9/11 tragedy. The people who have lost someone during that time have their own way of dealing with this, yet it is a huge deal that they have to be a part of. I have never had this type of thing happen to me, so I’m interested in knowing other peoples thoughts on this.