Trackbacks, and related protocols like WebMentions, exist to notify websites when other websites link to them. But the HTTP Referer header does this already, and is baked into the existing stack. So why do people use Trackbacks and other systems like that? How are they better than HTTP Referer header, and how do these benefits compare to the complexity trade-off?
I understand that the Referer header is frequently spoofed by spammers, hoping to get links inserted into web admin dashboards. But the same is true for Trackbacks, and presumably also true for other competing protocols. So unless the primary purpose of these systems is to combat spam in some way, I am guessing spam has nothing to do with it.