The wealth gap comes down to portfolio diversification versus concentrated leverage. Robinson didn't just act—he invested heavily in art, real estate, and business ventures that appreciated over decades. By the 1960s-70s, his net worth had become a compound machine: acting income fed into tangible assets that generated passive returns. Cagney, conversely, made his fortune through aggressive salary negotiations and profit participation deals in the 1930s-40s, but those were one-time windfalls tied to specific films. He won battles with the studios but didn't build the systematic wealth-generation infrastructure that Robinson constructed.

Cagney's career strategy was also more adversarial and career-limiting long-term. His reputation as a difficult negotiator and studio rebel meant fewer roles in his later decades, whereas Robinson's collaborative temperament and willingness to work consistently kept him employed and earning through his 80s. That staying power—seven decades of compound income—is where Robinson's advantage crystallizes. Cagney retired earlier and stepped back from Hollywood, cutting off future earning potential, while Robinson kept working and kept compounding.

There's also a timing advantage: Robinson's peak wealth accumulation happened during the postwar economic boom of the 1950s-70s, when real estate and art investments skyrocketed. Cagney's primary earning years were during the Depression and WWII era, when wealth preservation was the goal, not expansion. Robinson didn't just earn more—he earned at the right moment in American economic history and had the discipline to convert that income into appreciating assets rather than just lifestyle spending.