He did not have to beg to rich people and businesses for funding in exchange for doing favours for them.

That's totally untrue. FDR was about as deep in with the military industrial complex and the financial interests as anyone on the Republican side of the aisle. The fundamental difference between FDR and Hoover was that FDR didn't surround himself with the most economically blackpilled advisors. He treated the Great Depression as a subject of scientific inquiry and tried a whole litany of approaches to get us out of it, while Hoover treated it as a test of his convictions and clung stubbornly to the most conservative panacea.

The Roosevelts profited handsomely from both the national rebound and the subsequent war. They profited from America's predominant position as industrial superpower, by the end of the war. But their profiteering came as a consequence of successful economic experimentation and strategy.

By sharp contrast, the Von Mises / Rothbard / Ayn Rand capitalist die-hards repeatedly ruined themselves chasing economic orthodoxy and had to keep coming back to the state and national governments for bailout after bailout.

It was the private sector's continued heavy reliance on public authority that gave FDR a free hand, not FDR's own personal fortune. For the next forty years, private industry struggled to see the kind of enormous returns of the pre-war era. The struggles against an insurgent global anti-colonialism curtailed profits internationally. Strong unions at home curtailed profits domestically. Private industrialists relied enormously on state contracts and federal interest rates to turn even marginal profits.

Not until the Volcker Shock and the decoupling of labor productivity from economic growth could conservative business interests reliably reassert themselves against state control. That unleashed private enterprise from public financing and allowed for the steady re-privatization of the economy under Ford, Carter, Reagan, et al. This is the point at which unfettered freely flowing campaign donations began to eclipse the usefulness of large local party organizations, and the national privatization of politics really took off.