It entirely depends upon how one defines "left D&D" as to whether I've left or not, so here's the relevant details to figure it out:
When 4th edition was being teased in online articles, and those fluffy little books I can't remember the titles of leading up to the release, I announced that my 3.5 campaign at the time would be the last 3.5 campaign I ever run or participate in. I was never really a fan of the 3rd/3.5 system, and was thinking that everything I disliked was going to be done in a way I would like in the upcoming edition.
4th edition came out, and as I played more of it each week I kept noticing things that I was jazzed about during the "tease" period were delivered on in ways I wasn't fond of (the best example I can give is Critical hits; the tease material said there would be no confirmation roll, which was true, and that crits would do maximum damage for the attack, also true, and that certain weapons with special properties like axes would add an extra die, which was not as true as I was hoping, since almost every magical weapon had some amount of dice tacked on whether it was an axe or not), and after a few months of weekly sessions the game just wasn't working for my group the way we wanted it to. I took 6 months off of the campaign to run other games and devise strategies to make 4th edition work for us, and we tried them out, changed out for new ides, tried again, and repeat. We took another break from the 4th edition game to play other stuff, and when Essentials products had come out we dove back in to try those out. They worked better for us, but I wasn't really interested in DMing 4th edition anymore, so another of our group took over the DM seat... and ended up running our last 4th edition campaign ever (he accidentally highlighted everything we weren't happy with about the system).
So we quit playing 4th edition, but that didn't actually mean we quit playing D&D. All throughout the time that my group was playing 4th edition, I also occasionally ran Rules Cyclopedia D&D and AD&D 2nd edition. I still do, even though we mostly play 5th edition since its release.
So maybe I never quit because I was always up for AD&D or Rule Cyclopedia, or maybe I quit during 4th edition, came back for Essentials and quit again, being drawn back by 5th edition (we participated in the open play-test as much as we could, and have been playing at least once a week since the day the Starter Set showed up at my FLGS).
If you do count me as having quit, then what it was that drew me back was new material aimed at people that prefer the early '90s and before style/feel of game-play.