It's interesting how so many of Eustace's negative traits stem from his upbringing. Even his overwhelming greed can be traced back to his early life.
The Bagge family as a whole seemed to have a very self-centered belief system, and believed that getting what they wanted was far more important than any sort of moral consequence, and that theft was an acceptable way to succeed in life. We see this with every member of the family, not just Eustace: Ma Bagge is consistently shown within the series to be a greedy, deceitful woman who does whatever she can to get what she wants, and Ickett Bagge, while not shown on screen, nevertheless followed this belief by leaving his family with an accordion that he himself had stolen from a sand whale. Even Horst Bagge, easily the most successful Bagge, tended to value his own ego and accomplishments more than anything else.
With this heavy emphasis on money being the most important thing in life, combined with an unconscious need for acceptance, it makes complete sense that Eustace would crave money, because somewhere in his subconscious he believes that more money = more love.