For my money (until someone comes along with a more persuasive suggestion), the early association of GMark with the Apostle Peter was likely at least one major factor.
That is Larry Hurtado’s answer.
The second reason is that the early Christian community was super smart. Super. Just super. Which is why they kept the things associated with Peter.
Actually, I think Mark was preserved for that reason and almost that reason along, although I think Le Donne offers an interesting take.
If you’ve read my book, you will not that I think Papias was arguing for Mark’s inclusion but really didn’t care much for it. And why? Because it contains only some things from Peter. Some, as in a lot of that stuff is not from Peter.