To quote a favorite movie, 'As Good As It Gets' , the things we want to make are "why cavemen chiseled on walls."   Toning down the drama, we make the things we do partially because we can, and partially because the things we see in our heads have an innate need to become real.  They ask us to make them.

Sometimes it's owed to necessity and other times it's out of vanity.  
Sometimes it's to help express a thought and other times it's just to carry some stuff around.
Sometimes it's a request from the outside and other times the genesis comes from within.
Sometimes it's all intended and other times it's a happy accident. 

In every case, the "why?" can be simply summed up:  "WE. ARE. MAKERS."