Comment spam is advertising performed on somebody else’s property.
The spammer does not build the blog, attract the readers, write the article, maintain the server, moderate the discussion, or earn the site’s reputation.
They arrive after all of that work is done and try to attach a promotion to it.
Google describes the problem bluntly in its current guidance for site owners. Spammers exploit open comment forms and other user-generated-content systems to place spammy material on sites they do not control. Google specifically recommends moderation, reputation systems, nofollow or ugc attributes on untrusted links, and other defenses. See Prevent user-generated spam on your site.
The tactic works because a comment section is not an empty textbox.
It comes with an audience.
The host supplies the valuable part
A fresh spam site with no readers has very little reach.
A comment under a popular article may be seen by real people, indexed by search engines, associated with a trusted domain, or at minimum processed by the site’s moderation system.
That is why old comment spam often looked almost absurdly generic:
“Great article! I learned a lot. Visit my discount pharmaceutical casino roofing cryptocurrency website.”
The compliment was camouflage.
The real product was the link.
Google has long warned that automatically generated comments and forum posts can bury legitimate discussion and expose a site to content it never intended to host. See Google’s earlier guidance on protecting sites from user-generated spam.
Readers and moderators pay the bill
Every junk submission has to be filtered somewhere.
Software rejects it. A moderator reviews it. A site owner empties the queue. A reader scrolls past it. A legitimate commenter waits for approval because the site had to tighten its rules.
At enough volume, the host may disable comments entirely.
That is the hidden damage.
The spammer wanted free exposure. The site responds by making genuine participation more difficult.
Comment spam therefore fits Spam Empires perfectly even when the individual message is tiny.
The sender’s strategy is not to build an audience.
It is to borrow yours until you put up a fence.