Take a look at something like rclone and it immediately becomes clear that the photo app vendors you listed have no interest in allowing their users to easily access their data programmatically from their services in any meaningful way.

Example: https://rclone.org/googlephotos/#limitations

Glaring example:

> The current google API does not allow photos to be downloaded at original resolution. This is very important if you are, for example, relying on "Google Photos" as a backup of your photos. You will not be able to use rclone to redownload original images. You could use 'google takeout' to recover the original photos as a last resort