There is a vocal minority of readers that think that way.
What happened in Endgame wasn't a plot twist. It was, as the title suggested, an ending. A real plot twist ending is something like Shutter Island or Sixth Sense, perhaps weaker but still sorta The Wickerman. Perhaps I remember wrong, but nothing I saw in Endgame was something that dramatically shifted the plot and made me look at everything that had happened so far differently. It was a painful ending, sure, but there's difference between general spoilers and plot twist spoilers. And Endgame also had, what was it in the end, 20 something movies with these characters building connections with them and hence not relying on a giant plot twist to make it interesting so actually sorta proving my point.
Plus, you didn't ask about people posting spoilers of your ending, you asked about people commenting on big plot twists in advance. There is a difference between general spoilers and plot twists. Yes, people care about spoilers, but I bet lots of those people still went to see Endgame. And how many people still watched Madoka Magica even knowing the twist premise? If anything the plot twist drew people into that.
I'm saying, once again, if knowing the plot twist ruins the entire story it wasn't a well constructed story to begin with. It's fur coat and no knickers. I would happily spoil one of my big upcoming plot twists right now and still be confident most of my readers would stick around.