No, the excommunication / reconciliation of Fr. Feeney is not the reason. Natural Catholic aversion to schism and heresy is, combined with the following:
1) Fr. Feeney strict adherence to the Extra Extra Ecclesiam Nulla Salus thrice infallibly defined dogma. One of its parts read:
"
We declare, say, define, and pronounce that it is absolutely necessary for the salvation of every human creature to be subject to the Roman Pontiff."
In the words of Fr. Feeney himself:
The gate of the Kingdom of Heaven in beatitude was opened for the first time by the entrance of Jesus. The keys to that gate were put in the hands of Christ’s Vicar on earth when He said to Peter, and his successors: “And I will give to thee the keys of the Kingdom of Heaven.” No matter what we do in the way of justification, we can never enter salvation unless we enter it under the leadership of him who has the keys to that Kingdom.
That flesh and blood Vicar of Jesus Christ is none other than the Pope, our Holy Father, a visible head for Christ’s visible Church. He is a man whom we can point to as the visible Vicar on earth of the visible Christ in eternity. He is as pointable-at now in time as Jesus once was when He walked the streets of Jerusalem, followed by Peter and His Apostles.
It is a defined dogma of the Catholic Church that no one can be saved who is not subject to that flesh and blood Vicar of Jesus, the Roman Pontiff. It is one of the requirements for salvation. Justification is useless for purposes of the Beatific Vision unless submission to Christ’s Vicar has been added to it in essential complement.
Pope Boniface VIII, in 1302, infallibly declared in his bull, Unam Sanctam: “We declare, say, define and pronounce, that it is wholly necessary for the salvation of every human creature to be subject to the Roman Pontiff.” A defined dogma can never be changed. It holds for every age; it applies to every generation, until the end of time.
If you do not have a belief in, and submission to, a visible Holy Father and a visible Church, with clear distinguishable marks, you will never get into Heaven.
That is why not authentic disciple of Father Feeney could become a sedevacantist and sedevacantists are not allowed in the SBC Third Order.
2) Sedevacantist heretical denial of another part of EENS via Baptism of Desire -> Invincible Ignorance
"
The Holy Roman Church firmly believes, professes, and teaches, that none of those who are not within the Catholic Church, not only pagans, but Jews, heretics and schismatics, can ever be partakers of eternal life, but are to go into the eternal fire 'prepared for the devil, and his angels' (Mt. 25:41)., unless before the close of their lives they shall have entered into that Church; also that the unity of the ecclesiastical body is such that the Church's sacraments avail only those abiding in that Church, and that fasts, almsdeeds, and other works of piety which play their part in the Christian combat are in her alone productive of eternal rewards; moreover, that no one, no matter what alms he may have given, not even if he were to shed his blood for Christ's sake, can be saved unless he abide in the bosom and unity of the Catholic Church." (Mansi, Concilia, xxxi, 1739; Pope Eugene IV, in the bull, Cantate Domino, 1441)."
Most sedevacantists here have gone further than any conciliar Pope in their diabolical hatred for EENS: They have actually made Baptism of Desire an infallible dogma of the Faith and accuse whoever denies BOD of heresy! but in reality, they are not defending the fallible teaching of Baptism of Desire at all (far from), but the pelagian distortion of it:
salvation by implicit desire for the invincible ignorant. At the end, there is not an absolute necessity of formally converting to Catholicism and entering the Church via Baptism. Any Jew can be saved as a jew, a moslem as moslem, and a hindu as hindu....In doing this,
they share the exact same liberal Cushinguite error of the conciliar Popes they reject and become faithful disciples of modernist Rahner and all destroyers of true Tradition.