10. Why Was Peter Capaldi The Only Future Incarnation That Appeared?
Because he's the only one announced so far! If that doesn't answer your question though, maybe it has something to do with the thirteen lives of a Time Lord: maybe the Doctor wanted to hide his extra lives from the Time Lords. Maybe hiding Gallifrey takes up all of your lives. Maybe it's significant that for years of claiming he has thirteen incarnations, he uses them all for his greatest act. Either way, it was a lovely idea for a cameo.