Why is there a Traditional Catholic movement?

Because of the abandoning of whole and undivided Faith (integral Faith) in teaching at all levels, from the local parish, to the seminary, to bishops and the Vatican.  Truth does not change.  If was taught before Vatican II was right then what is taught now is wrong.  This is why people speak of "Rome's conversion."  

You cannot have the same religion as you did before, when the leaders corrupt the rites of the sacraments.
You cannot have the same religion, when unbelief is taught in the seminaries
You cannot have the same religion, when religious indifferentism is implicitly accepted and approval is shown for unbelief at the highest levels of authority.
You cannot have the same religion when moral teachings are reduced from requirements to salvation to thing that it might be "nice" to do.
You cannot have the same religion when people who claim to be your authorities despise those who are actually practicing that religion and testifying to their Faith, while they show they are endlessly willing to please those who are against the Faith.

This is why a practical agreement is impossible, and anyone who is really a Traditionalist can understand why, if they have the facts.

What is happening is there is a great increase in moral laxity and indifferentism, the SSPX has become less about being Catholic and more about being a social club with something of a cult mentality.  Why do I say a cult mentality?  Because the leaders change their tune from one week to the next, speak out of both sides of their mouth, and the followers accept this double-mindedness blindly, based "authority" which has no serious canonical support, only the claim of justification based on the threat posed to the Faith.

It's important to understand that the matter of how one must deal with the conciliar religion is very simple.  It's not the same religion It's exactly as Archbishop Lefebvre said in the following video: