I don't think you are being unreasonable to be disappointed by the response. As others have said, a lot of seemingly small examples of sexism put together form an all over all picture of deeply ingrained and institutionalised sexism.
But perhaps not everyone feels able or ready to engage with that "bigger picture." It can feel less threatening, less worrying to frame it as "don't sweat the small stuff," or write things off as being silly and insignificant. That bigger picture is damned worrying, upsetting and can be hard to look at, wholesale.
However, don't forget that there are lots of folks who lurk, who will have read the link and thought about it, even if they didn't feel they could comment on it. That may have sparked off something for them that will be added to the next thing they see/hear/experience, and then the next, and the bigger picture will start to develop. So, it's always worth posting something, raising an issue, sharing your thoughts, because you will never know how that might be reaching someone who is in a place where they need to hear it.
Also of course also important to post about things people can do to tackle sexism - campaigns, petitions, groups, stuff like that, so as the consciousness is raised, women feel like they can channel their frustration into something positive, something to make a difference.