There is always more to be said, but you can find some answers here.

After the fall of Quebec in 1759, the British granted the French generous language, religion and property rights, which were confirmed in the 1774 Quebec Act. This legal and political protection ensured that the Canadas retained its French and Catholic identity. This was considered intolerable to the mostly Protestant and virulently anti-Catholic New England colonists.

The Acadians, who lived in the coastal Maritime regions of New France, didn't receive such protections and were forcibly deported during the Seven Years War, with many resettling in Louisiana, which itself was an amalgam of Spanish and Creole cultures. These settlers evolved into the Cajuns of today.

After the American Revolution, the French settlers in America who now found themselves beyond the British frontiers of the Canadas, would not have the legal protections of their Quebec cousins. They would soon face waves of English Protestant settlement across the west. Outside the larger centres like New Orleans with established French communities and west of the Mississippi Valley, the pressure on sparse French settlements to adapt and assimilate into the dominant Anglo-American culture would have been intense.

Quebec's identity had always been uniformly French and Catholic, as Protestants were forbidden from settling in New France since the 1600s. French Protestants or Huguenots were banned in New France, but were allowed to settle in the US.

French America was not as culturally homogenous as French Canada was.

You might be interested in a similar question here with a couple comments by me as well as a great answer by u/firedrops. Part of the difference is that unlike Quebec, the French-speaking communities in Louisiana speak different varieties of French, as well as big political shifts in Louisiana after the US Civil War and World War I to anglicize the state and outlaw French usage.