When the DL is a sieve, a legitimate threat to run tends to make everyone else on the defense hesitate, including pass-rushers and mmbers of the secondary. The RPO was specifically designed to create and exploit that hesitation.
When that run-D deficient defense also has lmited personnel at LB capable of both coverage and run-D, it's only logical to compensate by using predominantly safeties in the secondary to help out against the run.
In the Superbowl, Foles and the Eagles coaches used their RPO run threat perfectly against a defense that simply didn't have the personnel anywhere on the roster who were capable of dealing with it effectively. There were no substitutions or adjustments available that would have made any difference.
This is the very last time I'll be addressing the subject. I'm on to 2018.