Fr. Fessio, while he was the head of Ignatius Press, was travelling throughout the USA and sending numerous fundraising letters, attempting to implement the "reform of the reform" in conservative NO parishes in the late 1990s. His missal/hymnal, Adoremus, was installed in whatever Church willing to introduce this idea. It was a miserable failure in the NO. (BTW, Fr. Fessio is a great friend of Cardinal Schonborn; they were Fr. Joseph Ratzinger's prize pupils at Freibourg University).
When Card. Ratzinger became Pope Benedict XVI. he turned toward Tradition as the instrument to bring about the reformed 1962 hybrid missal. This must be the real reason he warmed to the notion of reconciling the SSPX. +Fellay was just the prelate to push this Trojan Horse into the SSPX and the Ecclesia Dei Groups.