Why Students Leave Class Early

It gives me a sense of awkwardness. The class ends at 2:20 but yet at 2:15 people are already packed and ready to go. I am still trying to take notes while all I hear is the sound of notebooks closing and the backpacks zipping up. At times I feel bad for the professors, they rarely know what to do other than continue with the class. Sometimes they are bold and will yell out a reminder that class is not over for another 5 minutes. This whole process that happens in a matter of minutes reminds me of somebody leaving before a dinner is over. As anyone would say this act would be considered rude. But this happens everyday on our campus and I am assuming around campuses across the nation. Shouldn't this be considered rude? Is this teaching students that they can leave a place whenever they want without thinking about the person that is hosting? The professors put a lot of their time into these notes and lectures and they deserve some respect.