Tony Vargas
Legend
My response is really no different than it was in 2013. Though nostalgia is a factor, it's not the underlying reason. People are nostalgic for the days of past games and past rules editions because the newer editions aren't giving them the game they want. The current games don't give them what they used to have. Whether that's because ideas of what the game IS have changed, or how it should be played have changed, or something else is really beyond my ability to pin down. When a new rules edition like 5E tries to at least in part to dress itself in 1E clothes it's clear that somebody, somewhere saw that they wanted and needed to get back something that had been lost, and thus the players that went with it.
Everything you just described is standard-issue fad-cycling. Nostalgia may not feel like the right label for those of us who have been with the hobby the whole time, but it's pretty close: the appeal of OSR is it's similarity to the game of the past...
D&D was a fad, fads flop, and when they do people always say they're dead & gone for good. Then the fad comes back, and people always say its here to stay.
But, really, it's only the popular perception that cycles, the core enthusiasts stick around through the whole cycle.