Self-promo (whether on HN, Reddit, Lobsters) or any social platform seems like the most randomly enforced thing. Popular people can self-promo all the time and never get penalized for it, even when it's super blatant. Other, lesser known people try to share 1 link and get banned, but sometimes they don't. /shrug
I know this seems like complaining that the world is unfair, and it is, but it should be called out more often.