The reality is people join protestant churches for a lot of simple reasons. They like the pastor. One particular doctrine appeals to them. They have a great youth program for their kids. Their worship experience is awesome. Traditional denominational ties have grown weaker and many protestants go church shopping. They look for a spiritual home much the same way they would look for a physical home. They take it seriously but they balance different considerations. You can't have everything. You need to choose something so you do.
So when a protestants asks why you became Catholic your first task is to respectfully communicate that this choice was not like that. That is was simple and yet very complex. That it involved none of those things yet it involved all of them. The simple explanations often sound insulting to protestants. Because I want true doctrine and true sacraments. Because I want to stop committing the sin of schism. The point is the reasons are very serious and a corollary of that is that your choice not to be Catholic is also a very serious one. It is a little bit like when someone asks "How are you?" Do they really want to know? Most of the time they don't.
Mat 6:33 says, "But seek first his kingdom and his righteousness, and all these things will be given to you as well." I think that principle makes this question harder as well. By seeking God's kingdom we get everything we wanted in a church when we were protestant:
- The right pastor? We have pastor with real authority from God to teach, govern, and perform sacraments in His name.
- Powerful worship? The mass is the highest for of worship. Offering the sacrifice of Jesus' body and blood for our sins.
- A shared story. Protestants are often bonded by similar history. I grew up with a church full of dutch Calvinists who's family immigrated after the WWII. But Catholics have the whole story of salvation history to share.
- A solid foundation for our children. Where else can you find a church that you know will be teaching the true gospel in a generation or two or three?
- Strong social action. Not every church is actively caring for the poor. Often protestants that have a heart for the poor find a church that focuses on that. The Catholic church has that as a big part of her identity.
- Strong on life and marriage issues.
- Vibrant spiritual community. This seems to be absent at first. We tend to judge people who have different spiritual gifts and devotions quite harshly until we get to know them. But difference is where the blessing is.
- Biblical. No church that I know of reads as much scripture together as the catholic church does. Especially if you go to daily mass.
- Spiritual gifts. When I was protestant that was big for a lot of Christians. Are miracles occurring? Is the gift of prophecy active? But none of those churches could touch the Catholic Church for the sheer number of miraculous stories that were attested by solid evidence.
The list could go on and on. If you get beyond the superficial things then the Catholic church becomes the best from almost any perspective you can think of. That is what you would expect. A supernatural church will be different from a natural church. It will ignore some things that consume natural churches. But in the ways that are really important it will be better.
So why did I become Catholic? Because the Catholic Church has everything. Because the Catholic Church has the one thing that is needed. The only thing it might be missing is you!