Video is absolutely the easier case - there's a lot more information to go on. A single blurry photo has lost information compared to the original, but you can theoretically recover that information in a video where you get to see the subject with a variety of different blurs/distortions applied.

Note that a limitation of this result is that it assumes a static scene, but that's already a typical limitation of most gaussian splat applications anyway, so it kind of doesn't matter?