I get it, and when Photoshop changed this default, GIMP followed with changing this workflow. It used to be different in older versions of Photoshop and Gimp.
Advanced user usually know exactly what they're doing, and opening a PNG or JPEG file, changing a few pixels, and saving it, should require as few key presses as possible.
I don't want the UI to get in my way when I open->edit->save.
'Opening a JPEG' is creating a new image and importing the JPEG to it. ctrl-e on first use will establish the export setting. It's two clicks if you really want to overwrite the original. I think it would be very easy to accidentally and destructively overwrite the original image file if it was different, when ctrl-e is in muscle memory.
I get it, and when Photoshop changed this default, GIMP followed with changing this workflow. It used to be different in older versions of Photoshop and Gimp.
Advanced user usually know exactly what they're doing, and opening a PNG or JPEG file, changing a few pixels, and saving it, should require as few key presses as possible.
I don't want the UI to get in my way when I open->edit->save.