Couple of reasons come to mind. Super Mario 64 was transformative to a lot of people that played it, and the game could be said to be pretty influential for how movement in 3D worked (even though it as noted wasn't the first). There's a vested emotional interest in really building up the significant nature of SM64 because it was so meaningful to them. Donkey Kong has a different issue in that those most interested in it to argue its place... are the ones most likely to know the history and cite something like Space Panic first.
Beyond the fact that pre-NES Nintendo gaming is a haze to lot of fans anyway, the 1981 Donkey Kong just isn't something that many people are deeply into, at least not the point of debating its merits in the first platformer space. Arcade fans like it but have loads of games from other companies to also discuss, Mario fans are aware of its historical contest while viewing it as far removed from the 2D SMB games they like, and the Donkey Kong fandom respect its notability but are far more invested in the Country games. Whether or not it was first just doesn't really matter to a lot of the gaming audience. (Heck there's far more visible excitement at DK94 getting added to NSO yesterday than for any other non-Country Donkey Kong title being put up, the 1981 arcade game included, which tells you where the interest is.)
It's like how a somewhat learned Disney animation fan views the Alice Comedies from the 1920s; however much they recognize their significance, there's not be that many that would get particularly impassioned if there was an article debunking its significance as a live action/animation hybrid.