Pokmon is at the height of popularity again, between TCG Pocket, investors buying up stock, and general increased demand for sets such as Surging Sparks, it's a crazy time to get into the hobby
While the other cards at the top of this list would likely be there regardless of their design, simply because of who and what they are, this is one that likely nudged its way to the top because of details in its artwork
Wizards has a history of waiting too long or trying something else first (see Hogaak and Bridge from Below) and unfortunately, what they did is condemn us to at least a couple of months where Oko, Thief of Crowns is definitely the best thing to be doing in Standard
In the wider games, Gyarados was used to show players what shiny Pokemon were, with a red shiny Gyarados being a minor plot point in Pokemon Silver, Gold and Crystal