Material heretics are not heretics, but Catholics erring in good faith. Everyone should stop using the term "material heretic" because it is frequently abused and leads to confusion.
I'm not sure how you come to the conclusion that material heretics are Catholics erring in "good faith"?
It's true that there are many souls ignorant of the true faith and with the prayers and sacrifices of the faithful, many will be converted, but the majority of people do not love the truth but love sin more, as Our Lord said.
Our Lord clearly stated "Seek and you shall find, knock and the door will be opened." So anyone who sincerely seeks the true faith will find it.