It kind of depends on what *leaving the fold* means. Does it mean leaving a denomination?
Well, since denominations are not Scriptural, nor is baptism into a denomination, they do not save, they are not encouraged at all.
1 Corinthians 1:11-15
11For it has been reported to me by Chloe’s people that there is quarreling among you, my brothers. 12What I mean is that each one of you says, "I follow Paul," or "I follow Apollos," or "I follow Cephas," or "I follow Christ." 13 Is Christ divided? Was Paul crucified for you? Or were you baptized in the name of Paul? 14I thank God that I baptized none of you except Crispus and Gaius, 15so that no one may say that you were baptized in my name.
So *leaving* or rather choosing to not affiliate with, a denomination is meaningless. It does not equate to rejecting Christ.
The only admonition about anything similar to church attendance is found in Hebrews 10:25
19 Therefore, brothers, since we have confidence to enter the holy places by the blood of Jesus, 20by the new and living way that he opened for us through the curtain, that is, through his flesh, 21and since we have a great priest over the house of God, 22let us draw near with a true heart in full assurance of faith, with our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. 23 Let us hold fast the confession of our hope without wavering, for he who promised is faithful. 24And let us consider how to stir up one another to love and good works, 25 not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day drawing near.
What's in a church name? Simply an identification of the organization that gives an indication of doctrinal position. It has nothing to do with anyone's standing in Christ.
Churches don't save. Jesus Christ, who died for us, does.
As for those leaving the fold....reasons vary for each from those I've spoken with.....many leave because they could not find the fulfillment within they are seeking...so then one might wonder what it is they are seeking and identify that.
Many simply want deeper teaching and the truth often is covered with so much ritual and such it never reaches the heart....they have not known ..”Be still and KNOW that I am God”. The to do list outweighs the relationship aspect of Knowing Christ on a personal basis. So they sense emptiness in the course of time....it's just not enough.
Meanwhile the enemy of men's souls stands on the side ‘waiting for whomever he may devour’......and is quick to pounce for those unfamiliar with his devices. Many do not have the word of God in their hearts to withstand the deceptions...and fall easily into cults, false religions, and various other organizations affording them “belonging”.
Oh the reasons people leave their church are many and varied for all denominations.....but those who are in Christ eventually come home to the faith which is only in Christ Jesus.... IF they are truly seeking Him FIRST and desire the Truth....again only found in Him.