Obsessed
Those who are stagnant, who never go anywhere or ask anything, those who suffer from a lack of growth and have never experienced an 'addiction' to growth in any form are those who fall by the wayside. Growth is 'addictive' to those who seek more in life, they grow just by being active, by experiencing new things, and with every 'growth' they attain there is only more to offer. Growth, if we define it as moving forward and experiencing 'more' in this world (thereby growing a human beings) is 'addictive' only to those who chose to move forward.
Though here I would like to pause and question the use of 'addictive:'
Addictive, in concerns to its connotations, reminds us of the negative: alcohol, cigarettes, drugs in all forms. Addictive, by extension, is a connotation of regression. Regression is the opposite of growth. My point is this, the phrasing- Why is growth addictive? Isn't the best way to express this statement. It should be: Why are we, as a people, obsessed with growth?
The American People are obsessed with progression, moving forward, growth... sometimes to a detrimental extent (such as prolonging life as long as possible because we can rather than questioning if we should through medical breakthroughs and technology). In our mere two hundred odd years as a nation we have gone from being a divided country fighting over slavery to a nation of immigrants, black presidents, woman running for president, homosexual marriages, and (while not 100% equal) pretty darn close to attaining an egalitarian era of living. There is no other country I would rather live in than this one because, no it is not perfect, but it is trying to be. Each generation seeks out a newer, better world to live in and this 'growth' extends to all parts of our lives.
As long as a person refrains from stagnant behavior, as long a they try to experience everything that they can within their single lifetime, than growth will remain an obsession for future generations.
Growth is an obsession for those who chose to seek it, because it reveals just how much there is still to go. As long as there is that gap between what we can be and what we are, then there will be a group of people seeking to erase that gap, to become all that we can be. Only those who refuse to see the gap for what it is become stagnant.