Many editors open a photo, change its details and save the picture again, which re-compresses a JPG. This one changes only the bytes that hold the details and copies the image data exactly as it was, so the photo looks the same and stays close to the same size.
Camera makers store extra details in a private block that other data points into, and moving anything can break it. The editor writes a new date into the space of the old one and adds anything new at the end, so camera details, the built-in thumbnail and color profiles keep working. When a photo also keeps its date, location or author in XMP or IPTC, as many photo editors do, those copies are changed too, so every app shows the same thing. A removed location is wiped from the file, not just hidden.
The date, time zone and GPS fields follow the Exif standard: CIPA DC-008, Exif 2.31.