5 Answers

Trees take a long time to grow because the vast majority of the tree's tissue must be created through photosynthesis which requires the tree essentially breath in Carbon Dioxide and absorb water through the roots. 

http://www.chacha.com/question/why-does-it-take-so-long-for-a-tree-to-grow

perhaps their petrifried of growing up..

Could it be that we are in such a hurry,Let nature take its place,

If you would like your trees to grow faster, you could provide a little fertilizer at some distance from the tree. A tree nursery worker may know exactly what you need. Trees do best in the weather zones they are most accustom. We have volcanic cinders here that many trees and shrubs cannot tolerate.   

Some grow fast, such as poplars, 50 years; others grow slow like bristle-cone pines, 5,000 years.