Last but not least, the design of a card can also influence its popularity
In a world with cards like Stormbreath Dragon and Polukranos, World Eater running around, six mana needs to buy you something pretty saucy to want to go that high
If there's no exiled card when Unidentified Hovership's third ability resolves (most likely because its second ability hasn't resolved yet), the ability won't do anything
Considering how few chase cards it boasts across the TCG, this Clefable card is likely to remain among the most valuable on its roster for the foreseeable future
Their Normal Summon can't be negated and nothing to activate in response to their Normal Summon
The modes are quite different from each other, too, but giving your whole team hexproof, while maybe slightly over the top as most spells only target a single creature, is a good bit better than just giving hexproof to one of them