Speaking for myself, I don't tell ANYONE in my real life how lonely I am. Almost everyone in my family is toxic and they don't want to hear anything about me, let alone be supportive. I have managed to make a handful of casual friends, but they are still only casual friends and I don't want to scare them off.
Yes, there are a lot of minimizing, thoughtless, self-absorbed people in this world. I think the fear of being hurt by these types of people -- of being minimized, ignored, rejected, made fun of, etc -- is a big part of what makes some of us so lonely in the first place. At least for me it is. But if I want to stop being lonely I have to get past it and realize that when somebody says something hurtful or treats me badly, that's really about them, not me.