I disagree. JWs believe in Christ's Resurrection, this event being the hub of the faith, the seed of the Gospel. However wayward Christians are beyond believing in Christ's Resurrection, does not nullify their authentic faith in the kernel of the Gospel.
As above I repeat that imo the Christian faith is belief in Christ's Resurrection as nonfiction historical fact. Support for every other authentic tenet of the Christian faith radiates outward from His Resurrection being real, and JWs and many others certainly hold to views that in many ways conflict with the authentic Christian faith.
It is because they do not submit to their bishops. Every JW assembly /community exists within a Catholic diocese, or in both a Catholic diocese and in an Orthodox diocese. They all have their bishops, and they all fail to submit to them. The bishops are the authentic pastors of the one Body of Christ, their office instituted by the Apostles, a process described and alluded to throughout the New Testament, especially after the Gospels. Being in communion with the Church is physical, and not only spiritual. We are one because of our shared faith, in Christ's Resurrection (including JWs and every other Christian who doesn't submit to their bishops), but we are also one by receiving the one body and blood of our Lord, in valid celebrations of the one Eucharist. Authentic pastors---the bishops---are required for the valid celebration of the one Eucharist, which "limits" Christians to Catholic and Orthodox parishes. "Limits" because they're everywhere.
The Church used to be in both spiritual and physical communion with each other, for centuries. We are the frayed end of a rope right now though, with only about 2/3 of us in communion as I've put forth (which is a communion that I have admittedly made up, based upon analysis of the liturgy of the Eucharist, and personal interpretation of what I see in both Catholicism and in Orthodoxy), and granting Catholicism as the authentic Christian tradition /Church (I know you don't agree, but just to further the point), then only half of the Church is "in full communion" with her authentic supreme pastorate, the papacy (which is Catholicism's authorized definition of Christian 'communion;' being in communion with the papacy, which entails being authorized to receive Holy Communion, the one Eucharist).
We will reunite. The world will fall to the Church. The stage is set, all the ducks are in a row, and the only thing stopping this or delaying it, is the Church herself. We don't require anyone else to do anything, we just have to do it ourselves, somehow. We are who has to do it, and we will do it.