Why doesn't the President want his tax returns revealed?

On Friday, President Donald Trump lost the latest round in a protracted legal battle with Manhattan DA Cyrus Vance, Jr. (Cyrus, Sr. was secretary of state under Jimmy Carter) over his tax returns.
               

"WAAAAAHHHHHH!!! I'm rich! I don't have to show my tax returns to anyone! WAAAAHHHHH!!"

The burning question, of course, is why Trump, who promised he'd turn over those returns upon being elected four years ago, is going back on that particular promise. It makes people think he has something to hide. Like the prospect that he's not quite as wealthy as he'd like people to believe. He has also sued to keep his college transcripts confidential. Most Presidents before him willingly turned over their tax records to show transparency to the American people. You can bank on Joe Biden doing just that if he's elected in November, to return to tradition.

Trump is suing, and is being sued. No other President that I can think of had that kind of legal trouble while in office. The tabloid stories about, for example, the late John F. Kennedy, surfaced long after his assassination in 1963 (bear in mind, ye scribe didn't see these headlines 'til I was a teenager). Richard Nixon was undone by the Watergate scandal nearly a decade later, but he was more of a pro-active President than Trump wishes he could be, and, realizing how much trouble he was in, opted to resign, retaining what dignity he had remaining. Trump has no dignity, no shame, no transparency, just secrecy out of fear of exposure. Post-administration, Nixon remained a respected figure. Trump? Fuhgeddaboutit!!

Even fictional millionaires like Thurston Howell III (Jim Backus, Gilligan's Island) and John Beresford Tipton (Paul Frees, The Millionaire) would engender more trust than Trump. Think about that.