For a card to become a sideboard staple, it either needs to be the single most efficient version of an effect (Natures Claim), have a particularly backbreaking impact on the targeted deck (Stony Silence), or be so broad as to have an impact in multiple matchups (Rakdos Charm)
If all of them are heads, this attack does 120 more damage
A shop buyer can sell the top chase easily, but the box becomes easier to merchandise when there are several cards that look good in a display case, binder page, or break menu
Each of these decks has a distinctly different power level, which means no matter the power level of decks at a random table of players, I have something that wont be over or under powered for the game people want to play
The format evolves but not in radical ways and the reason behind this is quite evident if you think of it