The main reason is curiosity.
In 2011, a man named Justin Stouder in suburban St. Louis pointed a laser at a helicopter and was arrested. When he was being questioned by the police, he said-
“I started off admiring the laser, and shining it to see how far it goes. Then a helicopter flew by and I made the decision to see if it would reach the helicopter. Obviously it did.”
Stouder was not charged, although the act was a felony and he could have faced 20 years in prison and/or a fine of $11,000.
Over 2,800 such acts happen a year.