Someone caught this on Discord and it's wild. UPDATE: Developer has responded
http://www.nintendoworldreport.com/news/66448/balatro-pulled-from-european-eshop-no-eta-for-return
The long arm of PEGI may have whacked one of the year's biggest eShop success stories.
Reports emerged on our Discord server this morning of a UK-based chatter attempting to purchase Balatro at 1130 GMT, even going so far as to reach the point of funds being added to their eShop balance. Before the purchase completed, the game was removed.
There has been no updates from the game's developers regarding the apparent ban. Although not confirmed, it is likely that the game's content (using cards to make poker hands in a roguelike) may have run afoul of the mandatory PEGI 18+ rating for gambling in games.
UPDATE 1:00pm EST: Developer PlayStack has issued a comment on their social media (here) reiterating that they don't have an expected time of return, but the removal was apparently caused by a unilateral rating change: originally the game was assigned an 18+ rating, but following discussions with the authority (not named but presumably PEGI) were able to confirm a 3+ rating.