It's a tradition from (probably) the first time someone put an engine in something and made it move. Anything with an engine gets a name. My mower is Fred, my DR Power leaf vacuum is Helga (big, grouchy, and burly like a german woman), my old beater truck is Cecilia (you're breakin' my heart!), etc. It gives you something to call them with kids around that won't get you in the dog house. Edit: Sorry, I read this as "Why does everyone name their trucks?" and not "What does everyone name their trucks?"