I wrote my previous response while in a meeting. Let me try to explain this better.
A photo-sharing platform and a file-sharing platform are fundamentally different, and their APIs differ correspondingly. For example, when you have a photo in a photo-sharing app, it is associated with various pieces of metadata, such as the MIME type, the size of the image, the file name, the title etc. You also have the ability to pull various sizes for the photos or resize them on the server, crop them, etc. All of these are very important while building out a gallery – you need image size info, cropping and titles at the least. Many of these key markers are not available in Google Drive’s API, which makes it unsuitable for use in a gallery (the same way that Google Drive itself will not show you a collection of photos as a gallery).