I noticed the same thing when I started doing only loot runs (I didn't shoot anyone, I'd just loot and GTFO). It used to be that running into PvP was pretty much expected but eventually the loot run matches went so that other players would sit in the open looting and nobody shot them, which is something you wouldn't do if you were in a lobby expecting to get shot. I wasn't willing to go as far as to assert that's the matchmaking algorithm but my matches have definitely become more peaceful as I've stopped picking fights with other players.