Well, think of it this way:

Someone asks to borrow $1 million from you. It's most of what you have, but you do it. A few weeks later, the guy tells you he'll never be able to pay you back. You go bankrupt as a result.

A hundred years later, your great-great-great-whatever grandson receives a visitor. He's here to pay back the million, plus interest. It will be good for your descendant, but it doesn't help you any.

The French at the time of the Revolutionary War had no conception that one day they'd be conquered and would need US help to get out of it; America was a pipsqueak little country at the time.

Well if France was so impoverished by what the US owed them were did Napoleon get the money to go and conquer the Iberian Peninsula, Italy, the Low Countries and half of Germany, and then try and conquer Russia, Egypt and India?

After the King fell to the Revolution, America and France continued to have disagreements.

Some 1790s French, and some Americans, were upset that the very young USA didn't help them militarily during the pre-Napoleonic wars that France fought with Austria, Britain, and others. There was supposed to be a treaty of alliance, and both were republics opposed to monarchy, right?

Presidents Washington, Adams, and Jefferson had to struggle mightily with the partisan divide over neutrality or involvement in France's wars.

Indeed. Adam's Federalists sympathized with England while Jefferson's Republicans sympathized with France. The Reign of Terror in France and French diplomatic misbehavior in the U.S. soured many here on the nascent French Republic. France's refusal to honor neutral shipping rights, and the infamous XYZ Affair led to a brief Quasi-War between the two nations ("Millions for defense; not a cent for tribute", or something to that effect). Adams' efforts to end that expensive and not-very-popular war led to a split in the Federalist party which allowed Jefferson to take the presidency and usher in the Era of Good Feelings.