I think adult Christians change denominations or worship with another denomination for one or more of four reasons.
In a sincere effort to approach our Lord, Jesus Christ.
For social purposes or rescue from congregational estrangement.
To be more in Christian family harmony with family member(s).
Or in answer to a irresistible call.
Some of these events have presented themselves in my life and I bless my Christian brethren who have welcomed or assisted me and my Lord who has blessed me in so many ways.
Anyone who seriously studies the Bible and still doesn’t find the answer for which he/she is searching will continue to search and eventually convert to Catholcism because it has the fullness of faith and is the Body of Christ here on earth. So many Catholics have such a close relationship with Christ, but it is a very private thing for them, as you say, perhaps they answered a call.