First, because personally I think it's bad etiquette to post an invite link publicly on large, open-access forums like Hacker News.

Second, because while the biggest decompilation Discord servers have effective moderation team and processes, the vast majority are just a server for a project from one or a couple of persons with <100 members joined. Such small servers don't have round-the-clock moderation or customized settings.

Third, because I regularly see phishing crypto spam posted in the smaller servers. Spreading invite links publicly carelessly increases the odds that these scammers find them and spam them.