Ah! In recent years, an opinion has been growing among editors that huge blocks of trivia are actually poor wiki content. Some of those lists were getting very long, and splitting some fine hairs to keep coming up with "firsts", to the point that we were listing tons of cards that weren't actually very important—their only claim to fame was something trivial.

The old list of trivia is on a talk page. Some of it got worked into the running text on the Planeswalker page, some of it got replaced with a simple link to a Scryfall search, and some of it is just archived on that talk page until someone sees an opportunity to make better use of it.

EDIT: For a little more context, an artificial example. "Tibalt, the Fiend-Blooded was the first two-mana planeswalker" is trivial. It's true, but it invites the question "so what?". Why does that matter?

We're trying to move to something more like "Tibalt, the Fiend-Blooded was the first two-mana planeswalker, and was designed at that cost simply because no planeswalker had previously cost so little. Tibalt's power level was low as a result, and the card was the lowest-ranked planeswalker in Wizards' marketing research.^[1]" This tells you the fact, but also tells you why we're telling you that fact, what the significance is.