I don't think that feature ever went away with power locks. My 2017 Mirage & my 2011 Subaru Forester will re-lock if you don't pull on a door handle within minute or so. I just tested my Mirage. Unlocked it with the remote, & it re-lock itself about a minute later.
My thought is - if you unlock your car accidentally (putting your keys in your pocket for example) & didn't mean for it to be unlocked, it would re-lock itself for you. Annoying I know!