My guess is that likely the reason he didn't rehash what happened in the Gospels was that it was because what was recorded in the Gospels for us, was pretty common knowledge to them, back in the days when Paul wrote his letters.
And my original response was that the WRITTEN Gospels appeared AFTER Paul was martyred and what was considered "common knowledge" was as likely to be wrong as it was right.
Then why did the Catholic church canonize it?
And why do Catholics then consider the Gospels superior to Paul's letters?
And if the writings of Scripture are that likely to be subject to error, then why are the traditions of the Catholic church not considered to be so?