As @rosesworkshop has said, when theme of the day started the idea was for it to use tags that people will already be using on their items, so it’s a low effort feature that constantly changes, and the majority of the time that’s still what we aim for.
Of course now we occasionally have tags which are specifically aimed at Theme of the Day, such as the favourite piece one, but in general we want them to be tags that anyone could naturally come up with when tagging an item. We want every shop on Folksy to have a chance of being included (when relevant) and not just those that know about the feature and have time to make changes. We also don’t want it to take tags away from their primary use - helping items get found in search by buyers. Instead we usually try to make them tags buyers might search, so if someone has a relevant item that isn’t already tagged with it, then by adding it they could also be improving their listing for search. It can help those sellers that don’t use their tags to learn what sort of terms are good to use (and understand that the format is ‘valentine gift’ and not #valentinegift as we sometimes see).
While people can change their tags to match the theme (and of course we expect there’ll be some of that, particularly when you’ve already got a similar tag that isn’t an exact match), we don’t normally pick tags that don’t already have some items, because there’s no guarantee that anyone will add the tag after we announce them, and we want to make sure we already have enough items for the day in case they don’t.
It’s not saying we don’t want people changing their tags when their items are relevant, but we do expect them to be terms some people are already using.
While know there are still some frustrations with things like clumping on the full theme of the day page, where we expect most buyers to see theme of the day is generally on that homepage section where 8 items show which are random, without clumping, and changing every time you refresh the page. Even if your item is last on the full pages, it still has just as much chance of showing on the homepage as the rest.