They are part of one of the cheapest competitive decks in the Pioneer format, in this case Mono-Blue Spirits, which costs just a bit over $100 to complete
Plus its a pretty cool card
Descent into Avernus works well with most red commanders
If you have cast two or more cards by the time Vayne enters the field, you cannot cast any cards that turn
This long-running legacy means that Knight is one of the most well-supported creature types in the game, making it an ideal choice for a type-focused build in the Commander format
Jet Medallion, Bolass Citadel, draw spells, tutors, and black cards that lack colorless requirements in their mana costs tend to work best with Krrik, as they help you stretch your mana and card access into ridiculously explosive turns that can win you the game on the spot if your opponents dont have access to any interaction