It's so no one knows where you stash is hidden.
Everybody has different reasons. Privacy, so no one can track down your truck and steal it, or break into it. Since a lot of people list their mods, someone can always be watching and go get a 5 finger discount when shopping at night. Someone could also take your info and create a false identity if you put out enough info, etc. In many states with a license plate you can get all the info on an individual. In Cali that used to be the case, until the actress Maria Saldana (i think that was her name) almost got killed by a stalker. Now only PD, and officials can look at your record (supposedly). I just don't trust anybody and I like my privacy. Believe it or not, we're not the only ones reading this info. I have nothing to hide, but you never know who's watching or why. It's like that old TV show used to say "Who knows what evil lurks in the hearts of men?"
In this age of the internet and everything being out there, I pride myself in remaining anonymous. I have done Google searches on myself and nothing comes up. That's the way I like it! Privacy now is worth more than gold.