Because if we are not “Here,” then we live either in the future or in the past, and what good is that for? “Now” is when things are happening, “Now” is when we experience joy, pain, fear and whatnot, “Now” is when life happens. Yet, this constant babbling brook of thought running in the background, which we fall prey to, are used to, and take for granted, prevents us from being in the “Now.” But it doesn’t have to be so, the mind is trainable. I read about a South American shaman, who had the opposite problem. He could not understand our Western mind frazzledness and was trying to comprehend how our minds function because he only lives in the "Now."
Actually, the ideal would be to be able to go back and forth between both mindsets. We need the Western capability of analyzing the past and mapping out where we want to go in the future – to make a plan with intent - and we need the Native “Being-in-the-Now” for all other times, when we are doing and being. For inspiration take a look at Eckhart Tolle’s Power of Now, as well as the Pachamama Alliance and the Eagle and Condor Story.