During production, it was cool to trash-talk the movie as a certain failure. Too expensive, it'll bankrupt the studio, etc.

Then when it was released, there was genuine admiration and critical respect.

Then it just kept on dominating the box office, month after month. When it got really popular with the masses and repeat viewings by teenage girls, it became cool to trash-talk it again as sign of snobbery. I'm much too sophisticated for this derivative, manipulative, sentimental pulp.

Then trashing the movie became so popular it was cool to praise it for its chutzpah, production values, and sheer audacity.

And so on. It's an insight into the human condition. If everyone loves what you love, then you don't feel a like a cutting edge hipster, so you gotta go do the opposite.