100% of the Catholics that I know who left the church...and I know at least 6 (including a nun)...left because they sought spiritual growth and a personal walk with Christ...and the Catholic Church wasn't giving that too them.
Do you really have to ask why people are leaving the church when only 12% of Catholics believe the Bible is literally true...when only 7% read their Bibles with any regularity...when only 17% think Satan is real...or only 9% believe that their most important relationship is between them and God?
Now...the numbers for Evangelicals and mainline protestants are not near what they should be...but you get some disgruntled Catholic with a hole in their heart who wasn't discipled very well (and believe me...with numbers like this...it AIN'T the people...you have a SYSTEMIC problem) and they will leave the church in a heartbeat for something they perceive as real.
People walked away from Jesus, and He didn’t trip arse over elbow to accomodate them. You may think He had some kind of shortcoming in the evangelization department, but He spread the faith as opposed to what others wanted it to be.