There is a reason for that ruling, because of the common baptism done in the other Christian churches that the Catholic Church accepts as valid baptism.
NO, that has nothing to do with it otherwise things would have been treated the same way in 1917. Heretics and schismatics had a common baptism in 1917 as well.
Things changed in JPII’s 1983 Canon Law because it is yet another example of the false ecumenism of the Vatican II Church.