The Innocence in "Ode"

Reading Wordsworth's "Ode: Intimations of Immortality from Recollections on Early Childhood" I couldn't help but understand and appreciate the first stanza best.

"There was a time when meadow, grove, and stream, the earth, and every common sight, did seem apparelled in celestial light, the glory of a dream."

I interpreted these lines to be talking of the innocence of childhood and how when we are young, everything in nature and all around us looks beautiful and awe inspiring. We, as children, are so lost in our own innocent ignorance that we can't see the bad so much as the good. We notice the beauty in nature and try to be a part of it by enjoying ourselves in it; laughing, playing, frolicking and doing all the other fun and innocent things that children do and not having a care in the world.

"It is not now as it hath been of yore;--Turn wheresoe'er I may, by night or day, the things which I have seen I now can see no more."

The second part of the first stanza speaks of how when we grow up we loose that blissful ignorance that innocence of childhood brings. We see the world for what it really is to the educated and grown up mind. We look around us and see not only the good and beauty in the world, but also the evil and devastation that has been wrought on it, mostly by the hand of man. Why is it that we cannot maintain the beauty of the world all throughout our lives?