Perot failed at buying his way into the Presidency. So did Bloomberg. Hillary outspent Trump 2:1 and lost the election. Harris outspent Trump 3:1 and lost the election. The idea that rich people thoroughly control the government doesn't add up. (Though people definitely get rich by getting into power. The Clintons entered the White House as paupers and emerged around $100m.)
The Clintons writing books and giving lectures is also irrelevant.
They don't cater heavily to poor people for votes. They use lies and misinformation to get poor to vote against their interests.
If the poor were actually being catered to like you seem to think they are, they'd actually have their basic needs met.
Why are we stuck with Medicaid and Medicare instead of having universal healthcare? It's not cost. We're currently paying more than other rich countries (which answers your 'domonating government expenditures' comment). Because the status quo helps the rich.
Single payer means perverse incentives endemic to socialism.