As a now understanding Christian of Penal Substitutionary Atonement and non Mary worshiper, former Catholic, I can say it’s because after 12 years of Catholic school education, I didn’t know anything about Jesus or what He did for me. My Christian Biblical church preaches the truth from the Bible and believes in the Bible.
I am certainaly not a liberal. I sought the truth and the truth has set me free.
as a former Catholic, i have to “ditto” your post...
Sad that in all those years you never heard "This is My Body, which will be given up for you" and thought about it.