Why are people jerks on the road?

I’m just wondering why people are jerks in the road? Why can’t they be nicer to the people in vehicles around them?

Tonight I was in my way home on I25 and was trying to merge from the HOV lane to the main Interstate. I saw an opening and started to merge in and the person driving behind that vehicle sped up and cut me off. He wouldn’t let me merge. 

That is just crazy. Everyone is in the same situation. Let a person merge and move on. It’s not worth the frustration.  

Every once in a while I encounter a person like this but it’s not the norm.  

When I’m at a sporting event and we are trying to get out of the parking lot, most are cooperative and when lanes of traffic merge everyone alternates. That is the way it should be. 

Everyone should be respectful on the road. It will make those stressful drives that much better.