I think many of us do stop with a grade-school level of understanding about our religions, so it's no wonder many of us reject them when we develop our critical thinking skills and become more experienced in the world. We wouldn't be satisfied going through life with a sixth-grade education; it's surprising we think it sufficient to use what we learned in Sunday school to get us through all of our adult life.
I think that if religious studies were treated to some extent more like other subjects, informing teens and young adults that there is more to it, that doctrine is not written in stone, that there have been lots of changes and variations in religous thought throughout the ages (and still today) and also expose people to comparative religions and writings of the mystics and sufis, then more people would develop religious understandings to suit them as adults.
It's not that you have to do theological studies to have a full religious life, or to put a Christian spin on it, an authentic life in Christ. But for many of us the simple answers do not satisfy and if we feel we that can't legitimately ask deeper, more challenging questions of our religion, then maybe that religion was not worth anything to begin with. Any religion worth its salt should stand up to the questions of an adult who looks at the world and asks, why would a loving God allow this to happen.
lunamoth