(1) Your average Nintendo gamer isn't into the modding scene whatsoever; they just want to play the latest version of Mario Kart.
(2) Their games really are good. So good people will bend over backwards to mod them (or, in the case of older titles, even just play them), despite the challenges. Particularly for games they grew up on.
It's not a mod, per se (and to some extent it's tacitly tolerated by Nintendo), but the Pokemon Showdown[1] battle simulator is one of my favorite examples of a fan-made gaming project.
Competitive Pokemon follows a couple different formats: there's the official Nintendo-sponsored format, known as VGC, which is played on physical game cartridges and uses rules set by Nintendo itself; and then there's Smogon, which is a community-led format with dozens of different metagames and tiers. Players (usually) vote on rules and bans in any given format, and games themselves are played on Pokemon Showdown's browser-based battle simulator.
What makes this so cool is that Pokemon Showdown is a 1:1 replica of how player-vs-player battles function on physical game cartridges—including random glitches and quirks from earlier generations. (Gen 1 Hyper Beam, anyone?) Nintendo hasn't brought down the hammer because Pokemon Showdown is no replacement for actually playing a full-blown Pokemon game, but it's an amazing way to preserve competitive formats from generations past. The DS and 3DS may be dead, but BW OU's weather wars live on...
(and the whole gog crowd, me included as well)
That map sent me in a rabbit hole of Doom modding that I simply was not even aware that existed and was active.
They market to children/toddlers who have no concept of corporate mascots. Their fans have nostalgia toward childhood characters/stuffed animals.
Have a good day, I'm closing this tab.