[chongli]

They do that to preserve data. If you’re making a complex image with all sorts of layers and masks and then you save to a JPEG, you lose all that information as the image is flattened and compressed. Saving in the native format lets you be able to open the file again at a later time and resume working without losing any data.

Users would be seriously upset if they made JPEG the default and the native format a buried option. People would be losing data left and right.

[account42]

Saving as XCF still loses the undo history so it's really a question of which/how much information is lost. Meanwhile if you have a single layer image and export it to PNG which preserves as much relevant information as saving it as XCF it will then still complain about unsaved data if you try to close it. Absolutely infuriating behavior that no real user ever asked for.