Because in some places -- the Los Angeles area, in particular, where there are an estimated one million evangelicals -- many of these people were nominally Catholic BEFORE their Christian conversion experience. They became Christians in an Evangelical context ("Protestant", if you insist), and their memory of their Catholic past is simply one of spiritual deadness -- "How come they never taught me any of this in the Catholic church?? It never made any sense to me, til my neighbor invited me to Bible study, and then... !!! "
They don't identify by denominations, because they soon meet others who have had similar conversion experiences, in the ranks of the Baptist, Assembly of God & other Pentecostals, Calvary Chapel, Vineyard, etc, etc. They immediately sense a spiritual kinship with others despite the differences of church names (and minor issues, such as tongues, the rapture date, etc). As a result of their easily recognized commonality of spirit, they are loathe to distinguish themselves from one another based on denominationalism, which is increasingly regarded as sinful. So they simply say, "Christians", as a catch-all name for the whole group. And they all listen to the same radio stations and go to the same Christian bookstores and concerts and dating websites.
Some Catholics will go into a rage at this supposed Protestant "sheep stealing", but, the cold hard fact is that the Catholic church, in many places (especially here in Mahoney land) is not doing the job -- they're not evangelizing nonbelievers and they're not even making believers of people BORN into their church! Instead, they sit back and let people blunder along the hellward road until a "Protestant" preacher or neighor or friend takes the time to present the personal call to repent and be saved. Not all of then join Protestant churches, either -- I know a guy who is drawn to the Evangelicals but feels compelled to stay within the Catholic church for family reasons, and I'm sure there are many others like him who stay Catholic but secretly owe their faith to the "Protestants".
I guess you might say, we are PROTESTING against the fact that the Catholic church didn't bother to teach us how to live Christian lives. Fortunately this may all change soon. B16 proclaimed a while back that "lack of Biblical spirituality is the root of Catholic problems", or something to that effect. If he follows through on that idea, millions of Evangelicals may return.
I understanding where you are coming from. I teach 8th Catechism. I've had these kids for 3 years now. I make/encourage my kids to look stuff up themselves.
Things I know I've taught them repeatedly, the next time it comes up I get a vacant stare. I have drilled covenant into their little brains. I'm just not sure it took. Some Sundays, seem like a waste of oxygen for all they seem to get it. So, it's not like some of us aren't trying. And it worries me, alot.