Am I the only one that could never get into any of the Smash games? I discovered the series on the Gamecube, but wasn't my cup of tea. People who think Smash will dethrone Mario Kart 8 Deluxe believe it will do so because they believe it's the "bigger" franchise, or because they say Mario Kart 8 Deluxe is just a port? Personally, I don't see the appeal to Smash but I guess I'm in the minority. Mario Kart is the ultimate party game for me. It's the only game everyone can pick up and play at social gatherings, that doesn't require reading, let's everyone have their turn in a reasonable amount of time, and that is just immensely fun.
It's funny because GameCube was exactly the one other time Smash Bros. outsold Mario Kart. Right now, people are thinking it might happen again because of Smash Bros. hype being at an all-time high, with insane first month sales, whereas MK8 is just a port, albeit sales don't seem to care.
And yeah, Smash isn't as good as a 'social' party game because it is a lot more complex than Mario Kart even at a basic level. I'm pretty sure you're not the "only one" who never got into Smash (come on), but it can't possibly be that hard to understand the appeal.