In a brilliant essay-comment here several days ago, Annika explains powerfully why some younger Catholics are forced to distance themselves from the Catholic church — in order to keep the faith they've been taught as members of the Catholic community:
As a young person who attended Catholic school from 5th through 12th grade, I would argue that most Catholic schools and Catholic parents teach "the faith." The issue, I think, is what defines "the faith."
Who gets to determine what defines Catholicism or who gets to identify as Catholic? Catholicism is not stagnant--it has always been and will always be changing, and it has always been and I hope will continue to be diverse. Like all religious traditions, it was influenced by the cultures surrounding it, and cultures continue to develop. Catholics aren't and cannot be separate from the culture that they live in.
Ultimately, as you point out, it is the local parishes, Catholic schools, and parents who are transmitting "the faith," not the bishops. For me, then, it is the lived experiences of the average Catholic which cause "the faith" to grow and change, not what a few clergymen have decided it should be.
"The faith" that I was taught by the teachers, nuns, and youth group leaders in my local community was based in love and compassion for all people. I was taught that, above all, the Church should be an inclusive place of true welcome for anyone who wanted to be a part of it. I was taught that all people were creations of God who therefore deserved respect and love. I was taught that economic and social inequality is wrong, that injuring people is wrong, that injuring the earth is wrong. This, to me, is the core of the Catholic faith, not whether somebody uses birth control or has sex outside of a committed relationship, and I think many/most Catholics would agree with me.
And so, "the faith" as frequently portrayed in parishes today does often seem "alien" to young people who were taught as I was. The values that they preach contradict the values that they practice. We hear priests giving homilies which are homophobic or Islamophobic or that assure parishioners that despite the words of Jesus and the practices of early Christian communities, they shouldn't have to share their wealth. We watch as LGBT parishioners are denied communion for being in a committed relationship that seems more devoted and has lasted longer than the relationships of most heterosexual couples at the parish. Old school friends come out and we learn that they once almost committed suicide because they believed Church leaders when they were told that they were "intrinsically disordered." We realize that the Church sometimes cares more about birth control and abortion than the poor or the oppressed. We slowly realize that, if we are female, we will never be considered by the Church as capable of being priests or even just leaders within our parishes.
Eventually, the hypocrisy catches up to us and no matter how much our Catholicism means to us, it is difficult to stay. Eventually, Mass becomes upsetting, not in a healthy way (for all of our consciences sometimes need to be bothered), but in a toxic way that just causes us to lose hope and faith. The "peace that passes all understanding" becomes easier to find outside of the Church than within it, sometimes.
We have to decide whether to fight for reform from within, or to leave and find community and faith elsewhere. It's a hard decision, and as each year there is seemingly less hope for Church reform, more and more young people cease being practicing Catholics.
Sorry for the length of this response, but hopefully I explained why some of us young Catholics are no longer going to Mass.
TL; DR: I don't think it's an issue of being taught the faith, but of the hierarchy/clergy betraying the faith and the values that young people were taught by faithful older Catholics and still believe in.
As I've said before, many of the comments that astute readers leave at this site on any given day are worthy of publication, and could compete with essays in academic journals. Annika's essay-comment is one of the best dissections I've yet seen of the quandary in which many of us who are Catholic find ourselves, as self-professed "orthodox" "traditionalists" inform us (often, with the overt approval of the pastoral leaders of our church) that their reductionistic, truncated, cruel reading of "the" Catholic tradition is the only show in town.
Leaving us with no choice except to distance ourselves in order to hold onto the gospel-based Catholic faith communicated to us through our religious formation . . . .