it appeals to the lowest common denominator by quite possibly having the safest points of appeal, there's nothing remotely scandalous and even go out of their way to not allow any r18 works of their characters, which means normies can love it without looking "weird" to others
>>715272057
a lot of channers play it but outside of here and other fringe communities globally its not that popular and contains too much contentious content for the wider public to enjoy it, it is what it is, its really only super popular in japan and korea for a reason

not sure why people think sans is harder than the knight, getting hit by the knight is brutally punishing (even with the cape certain attacks can still chunk massives amounts of health from the team, and there's rng elements up the ass in some attacks that can fuck you over), while sans lets you quickly adjust if you fuck up and the majority of his attacks don't have rng
having 3 potential actions per turn doesn't make that much of a difference when your only real source of damage is susie and she needs to be constantly fed tp and kept alive, and you optimally want at least kris alive to feed tp and use items if you fuck up