Because he's a megalomaniac with deep-seated feelings of insecurity.
Which is the same reason for everything he has ever done.
He must outcompete all others constantly, in his quest for self-fulfillment, accumulating ever more wealth and power along the way.
After each victory, the spectre of insecurity emerges from its hiding place deep within his psyche.
Deep inside he knows that "he will never be good enough" to satisfy the many mental "demons" which affected his early development and will never let him "rest on his laurels".
Bloomberg's motivations for becoming a "business maven" do not necessarily reflect negatively on his honesty, character, or positive contributions to others.
And it is quite possible that my analysis of the man is completely off base; maybe he's just in love with money, businesses, and partying with beautiful women.