Because neo-nazis have essentially perfected coopting “respectability” politics in public online discourse. Calling out dogwhistles can have a nasty blowback effect because they’ve manufactured cover (eg “I’m just quoting what [a party with unknown intentions] wrote on wikipedia!”) that gives them footing to claim misinterpretation at the mildest, or outright persecution in other cases.
HN is actually a really interesting case for this stuff, because the Primary Sin here is “violating decorum”. If I wanted to A/B test hateful dogwhistles, this site would be the perfect place. Nobody is allowed to post “Fuck off nazi/tankie/[insert other toxic group]”
Respectability and Decorum are how we open the door to obvious but just-subtle-enough crap like that.