To clarify, all the tags were added by the community, Leaf just gave special status to some of them. You can always add a new one, but if it's too specific and nobody else uses it, what's the point. For instance I have the tag "urban" on a couple of my games. You'd think someone else would have used it before or since, but no. Something like "still life with flowers" will be even less popular.
That said, devlogs are very effective as a marketing tool. And promoting outside of Itch.io is important too.