Because sado-evangelism is "Satanic" in the truest sense of the word. Its primary characteristic is accusing the brethren.
It certainly isn’t always the spreading of “good news” (the meaning of the word Gospel).
A lot of the “spreading” is telling Catholics they are doomed—I tell you-—DOOMED.
HO! That’s really a hoot. RC’s just don’t like it when their sacred cows are discovered and brought out into the open. It’s GOD who WANTS us to evangelize, yes, even to evangelize Catholics who are going down the wrong road with so many heresies.