Timing. Last week I moved some downloaded images from a dying device where the USB port was no longer reliable by copying them to Google Drive and was surprised to find the images showing up in Google Photos.
Turns out I wasn’t the only one who found that confusing.
Now, Google is disconnecting the two services from each other so that when you upload to one service, you know which service the file is going into.
https://www.blog.google/products/photos/simplifying-google-photos-and-google-drive/