It's not about being unable. Readers here recognize sarcasm, but they also recognize what happens to a web forum where it is allowed to proliferate. That's why https://news.ycombinator.com/newsguidelines.html asks commenters not to be snarky on HN.

Lame internet humor tends to grow like kudzu, and the users who post it underestimate how lame it is, as scott_s pointed out well long ago: https://news.ycombinator.com/item?id=7609289. Sarcasm isn't quite the same but it's related.