The film is a metaphor for how social-media groups fall apart and expire.
When initially created, many people participate in a hashtag/facebook group/message board/whatever, commenting regularly and getting along. But before long, individuals start to lose interest and drop out without a trace. As the group dwindles, members get on each others' nerves, and some leave because they feel attacked and/or ignored, or just can't put up with others' crap anymore. Eventually, there are only a handful of people left, struggling to maintain an interest and keep other members from abandoning the group. Finally, when the last stragglers' effort to attract a new crowd fails to retain any new blood and too much personal enmity and drama has come to the fore, the final members quit coming and the group shuts down.
At the end of the movie, it was Claire who disappeared, not everyone else, and an empty version of the normal world is where each person who gets vanished goes.
- No one else could see her when she doubled over in the car.
- The emergency response team and the Men in Black types would have had to work really hard to all look away from each other at the same time, so although whatever is going on is not necessarily logical, it still makes more sense for her to be the one who got vanished.