Because all things are transient. Developing attachment to too many things will be pointless in the grand scheme of life.  Material things will always erode, decay and lose value over time. People's perceptions will change about them as well. 

Too much complexity in life causes stress and dissatisfaction, it leaves no time for family and friends and leaves no time for you to do the things you truly enjoy. 

As the human race evolves into a new technological era , things will become easier but also more complex. People will always be wired into "the network" and will have no time to observe simple things that humans really need to observe. 

We may build great things and advance so far in tech that our minds are literally on a network but in the end we do not know what mother nature may choose our fate to be and it may all turn to dust once again (unless we colonize a different planet).  

So in conclusion I believe that complexity is necessary to advance but must always be balanced with the simple things in life.