At the beginning of Bill and Ted's Excellent Adventure, Rufus explains the Utopian life that Earth now enjoys and that it's all thanks to inspiration from the music of the band Wyld Stallyns, but that it all might never have come to pass had the band been forced apart as punishment for failing a history presentation. So apparently now he must go back in time to help them pass.
Since Rufus himself lives in the world where they formed the band and created low-mini-golf-score world, why does he feel the need to go back in time to help them pass the test?
The obvious answer is that history also records the pair passing only with his help and therefore he must go back in time to fulfill that destiny.
But if you think of it as that kind of loop, there must be a beginning-world where Wyld Stallyns were forgotten (akin to "Loser-George-McFly-World" at the beginning of Back To The Future), but for some reason Rufus decided to go back in time and help them pass, as if he knew that this pair of nobodies would turn out great music that would inspire major socio-economic reforms.
How could this happen?