Its out of spite... They see you parked so far away so just park next to you to mess with your head..
Its the same as when I get to a parking a a guy has purposefully parked over 2 spots.. no worries, I will just park my passenger side as close to his/hers drivers door as possible while still being in my parking spot.. Had it the one day, & the guy goes & climbs in the passenger side across to his drivers seat.. I was still in my car...