In NCIS, Gibbs never locks his house. I've always thought that it's a fun quirk, but has there ever been an explanation of his thought process behind it?
Because it has no lock, duh.
No, there has been no stated reason why Gibbs doesn't care about locking his house, in universe or out of universe, aside from the story telling reason of being able to have random conversations.
It has been this way since season 1 Episode 2 where DiNozzo first learns this.
In Season 7, episode 3, Tony even points out there is no lock, meaning it can't even be locked if they wanted it to.