When people start to get to know God’s Word for themselves, they for the most part realize that the Catholic Church got far away from it. Even just knowing the Gospel and getting a sense of what it promises tends to turn people away from the Catholic Church in droves. There are some who turn to it for reasons like pride in that they believe there’s something good in themselves, or that they like how much the Catholic Church embraces the wisdom of the world and beliefs like evolution. But overall, if you have once and for all surrendered all you are to the Lord, understanding that there’s nothing to trust about your own nature and that He wants you to live in continual dependence on Him, then you understand that if you have completely given up on yourself, He is all you need and will take care of you, and He will bring you into fellowship with those who also have given up on themselves and surrendered to Him.
I can say this because I am a revert to the Catholic Church. I left, due to poor catechesis, embraced the lie of anti-Catholicism, and then after a thorough investigation and God's grace came back.
And plainly people leave for two reasons, poor catechesis, or unconfesed sin. anything else they tell you is a lie to make themselves feel better.