Willie Sutton was right.

US banks are rolling in so much dough they are begging regulators to let them return to the days of risky proprietary trading — all the while stiffing their interest-starved customers, critics say.

With cash deposits surging 50 percent at the top three banks since 2012, critics say it’s time the banks finally cut a break for retail customers.

A record $1 trillion more cash is on hand now than in 2007, before the financial crisis.

This princely sum languishes in American bank vaults largely because of strict Federal Reserve liquidity requirements, according to one estimate. Bank profit margins are also on a nice rebound.

But forget about higher interest on your savings, or lower service fees on checking. It’s not happening soon, analysts say.

“Banks in the US have a staggering amount of capital — hundreds of billions of dollars in cash. You’ve got a half-trillion of cash and securities alone sitting at JPMorgan Chase,” Dick Bove, chief strategist at Hilton Capital Management, told The Post. “In fact, there’s only one company in America that made more money than JPMorgan last year — and that was Apple.”

Ten years after the $700 billion taxpayer-funded US bank bailout, retail customers are still being bled bone dry with steep charges and ultra-low yields on savings, data reveal.

“It’s shocking and unacceptable,” said Michael Kink, executive director of the Strong Economy for All Coalition and frequent critic of US banking practices.

The typical rates on savings accounts and 9-month CDs are at miserable, all-time lows, barely hitting 1 percent — though at other banks and no-frill outfits, rates can hover around 2 percent for longer maturity products. But even at that, critics say these rates are hardly a bonanza.

Meanwhile, service fees on interest and non-interest checking account have soared — from an average of $11.72 on interest-bearing accounts in 2007 when banks were on the brink, to nearly $15 today, just when banks are flush with money, according to Bankrate.com. Fees on non-interest checking accounts have more than doubled in the same period.

“There is no happy anniversary for retail customers 10 years after the financial crisis, because savers are still being penalized due to low interest rates,” said Mike Mayo, Wells Fargo Securities managing director and head of US large-cap bank research — though he was not specifically referring to his bank.