text: The number one reason why people don't use a cellphone why driving, because its causes car crashes. You have to keep your eyes on the road at all time or it will lead to jail time!!! Driving under the age of 18 is illegal in most states. Another way that its dangerous is if you are drinking and driving. Which means that more people or dying each and other day. Reports have that 1.6 million crashes are caused because drivers text while driving.