Catholics become Mormons because they are seeking something better than what they think we have. It’s a sad truth, but rather than looking deeper into their own faith for answers, they look outside and listen to the naysayers.
Often it is because we (parish and nuclear family) did a poor job educating them in the Catholic faith. Perhaps the CCD program was shallow and all-inclusive to the point of triviality. Perhaps the parents weren’t concerned about ensuring the kids received a proper religious education. Perhaps regular Sunday Mass was simply not a priority.
Sometimes something bad happened that caused the young person to turn against the church. And sometimes the young person is in rebellion against his/her parents and rejects both their authority and the (rules, rules, rules) authoritarian church.
Whatever the reason, the Catholic in question is left with a void in his/her life, and has begun to recognize something is missing.
Along come the missionaries, nice, polite, well-dressed fellows who have the outward appearance of a fellow Grandma would approve of. They bring a copy of the Book of Mormon. (Oohhh! Secret knowledge the Catholic Church refused us!)
They also bring a tract saying, “You can know this message is true. If you ask your Heavenly Father in prayer, you can receive an answer from Him through the Holy Ghost… The Holy Ghost confirms the truth through feelings, thoughts, and impressions… These feelings from the Holy Ghost are personal revelation to you that the gospel of Jesus Christ as restored through Joseph Smith is true.”
There you have it. Hook, line, and sinker. This is the ultimate “warm fuzzy” religious message.
Pretty scary that someone would fall for it, but it happens every day.