Why is Cayden Cailean the only god with a last name?

[Yqatuba]

I'm guessing because he was one of the Ascended, but if that's the case why don't the other Ascended have last names?

[Gorbacz]

Because they've discarded their names when becoming deities. Cayden felt like he likes his enough to keep it.

[deuxhero]

Some ideas:
He did ascend over 1000 years after Iomedae. Perhaps family names weren't common?
Iomedae seems to have born a commoner (not entirely sure on this), though we know little about how Cayden came to be a mercenary. It's possible he was from a family important enough to have one.
Perhaps they both had family names at some point but "Cayden" was relatively common (perhaps shared by someone notable then but now largely forgotten) and Iomedae not (it certainly sounds like "Cayden" would be more common), so people dropped hers but not his?

[Gug on the Silver Mountain]

Thamir Gixx always has the Primarch's surname.

[Yqatuba]

That makes me wonder: is there anyone else in the setting with the last name "Cailean"?

[Zhangar]

According to Cayden's deity entry, Cayden's church runs many orphanages, and it's not unusual for the orphans to take Cayden's last name as their own.

That being said, I don't recall any NPCs in print following that naming convention.