This is an excellent example of the sometimes-uncomfortable truth that while the games industry is finally becoming mainstream, it has a long way to go before it matures.
The games-as-art movement has always been underground, and the independent scene has always been willing to defy convention (particularly in increasing diversity), but more and more developers are seeing parts of the industry close off in favour of serving larger publishers.
What we're starting to see is a serious increase in profit-seeking, bureaucracy, and corporate dissociation in the secondary industry surrounding the gamedev scene, which can only harm the indie fringe.
It remains to be seen whether the industry as a whole will continue to follow the trail blazed by independent developers or whether the shutters will come down further. Will art-house indie games be able to survive alongside massive blockbuster AAA titles? Or will the "mainstream" games industry go the same way as film, with Hollywood productions eclipsing everything else?
This is why Lee says some developers and other attendees feel left out. Many who attend Lost Levels are making games that don't receive mainstream recognition, but they feel their contributions are on the bleeding edge of gaming and therefore worthy of just as much attention and discussion. Using tools like Twine or GameMaker, they focus on individual stories and authorship to make games that expose human stories and vulnerability with an aim to evoke empathy, not just fun and not even necessarily a profit.