Why is it considered schismatic if a group wants to stay true to your ancient traditions?
It's not. Or...it shouldn't be.(I'm sure some crank will want to announce I am going to Hell, etc.). It only became an issue of schism in the relevant disputation to the extent that the groups following Archbishop LeFevre apparently defied papal authority, etc. Vatican II, as a council, did not authorize the complete elimination either of Latin or the traditional Mass. The problems have been associated with liturgical attitudes and how extreme the disagreements between the two sides have gone. For instance, rejecting the entire council, sedevacantism, theological questions about the nature of the new vs. the old Mass. At ant rate, traditionalists can observe the "indult" Latin Masses within the existing structure of ecclesial authority (i.e., JP II, etc.). The continuing arguments tend to get bogged down on who bit whom first, etc. We await a new Thomas Aquinas who will be able to set this all in writing with the relevant theology, canon law, conciliar documents, liturgical histories, and disciplines explained with clarity. Anyone who reads through the text of the old Mass really ought to be able to see that there is nothing wrong with it and that it expresses Catholic worship in prayerful and dignified solemnity.