Probably because so many of us were taught that the Protestants are radioactive and we need to steer clear of them. Back in mother’s day, she was taught in no uncertain terms that all Protestants WOULD go to hell. Not true Church teachings, perhaps, but it scared the daylights out of her for her Protestant friends, and I’m afraid this mentality hasn’t worked its way out of the Catholic population.
I would never have come back to the Church after my hiatus a few decades ago if it weren’t for certain non-Catholic preachers. I actually learned my way around the Bible from non-Catholic preachers. Never even wanted a Bible until a TV preacher showed me how incredible its contents were. In 8 years of Catholic grade school they substituted social issues and political propaganda for religion, so we didn’t learn anything. My Lutheran friend could run rings around me in terms of what’s in the Bible.