Image in Photos has a bigger size after it was saved from Files app

Why the image, that was saved from Files to Photos, has bigger size that such in Files?

Steps to reproduce:

1. Download any image from Safari to Files
2. Open the image in Files, click the Share button, click Save Image in opened menu
3. Then go to Photos, open the saved image, click the Share button, click Save to Files option.
4. Open the Files app, there will be two the same images, but both will have different sizes in kilobytes.

iOS 13.3 / 13.3.1