I think it does this after the photo has already been stored as JPEG. I think users would expect the image be persisted the moment you capture it, so any transformations after that are better done in metadata. When the image has been saved as JPEG the original image data is discarded so you can't transform without deteriorating the image.

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dividuum 3 days ago | parent [-]

Pretty sure you can rotate JPEG images lossless. But it’s still simpler to just modify metadata.

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perching_aix 3 days ago | parent [-]

A quick search suggests to me that it's only a lossless process if the image dimensions are a clean integer multiple of 8 or 16 (as the blocks can be 8x8, 8x16, 16x8, or 16x16), otherwise the edges must be reencoded. Never written a JPEG codec though, so happy to be proven wrong.

	▲	addaon a day ago \| parent [-]
		This is true, and others have mentioned it, but I think people are underestimating just how universal sensor dimensions being a multiple of 16 is — I really can’t think of any exceptions.