Overwhelmingly, people follow the religion of their birth. Once a Catholic, always - even if you don’t attend church any more. Catholics rarely convert out, even the uncommitted ones.
If they’re uncommitted, they don’t really care either way. I suppose if you’re truly apathetic about religion, you just stay with what you have. If you cared to reject it, then it means you’re not fully apathetic, and you care about what you believe at least enough to reject it (and call yourself a non-believer or an atheist).
I can’t speak for the statistics (I’m just going on your word here), but I can say that in my search I have found Catholicism to be authentic at least in regards to true Christianity. If Catholicism is not true, then it calls all Christianity into question. Why would any of the later off-shoots have any more credibility? So, I’ve concluded that if there’s anything to Christianity, the Catholic church is probably the true one (with a small chance of the Orthodox Greek or some other very similar one being more correct). I do like the Quakers, though.
If Christianity is wrong, then the next most similar, historically-authentic religion would be Judaism. I could see belief in that, but then you’re left without the new testament, with a rather older religion. I find that unsatisfying. Islam is more “structured” with more silly rules than Christianity.
I have difficulty believing in any recently–]invented/-] “revealed” religion. I mean, where was God all this time? So that leaves out Sc-Fi-tology and all the newer stuff for me.
I suppose what makes more sense then would be some form of Hinduism, though there seems to be a lot of mythology involved with it, or the simpler Buddhism. But then the very focus and goal seem to change (it’s not about God, it’s more about you and your happiness). From there on out you get into spiritual philosophies, maybe new age, then more psychological/secular and finally totally atheistic philosophies.
I am still on an intentional spiritual journey (as I suspect you are), but so far I find lots of good reasons to stick with Catholicism if I am to consider religion at all (versus the “spiritual but none of that icky religious stuff” people). I have found things I don’t understand or maybe don’t fully agree with, but I haven’t found the very shaky foundations you do in so many other forms of Christianity. And for the most part, it is a very coherent and “open-minded” religion while still retaining a two-thousand year old tradition and dogma.
I would have “switched” by now if I had been born into Jehovah’s witness or a protestant church, for instance. Maybe not if I had been born into Buddhism, since its a totally different belief system.