I'd say pad and stick aren't so different for people, but the capcity to train people is probably harder in KOF since it's about learning the game's system rather than a single character. And that can be pretty overwhelming for a new person. Execution is harder than most games too, as SF is looser (even if KOFXIV is easier than previous games) and because of that can appeal to more people.
But the lack of focus from the community is a fairly big problem. It's hard for people coming in to figure out how to pick a character, and there isn't many forms of material en masse like, say SFV or even Tekken. GG has gotten way better ever since Rev came out along the lines of introducing new players to their concepts. And while that material is out there, content like that needs to be repeated and continuously made. You'll see seven people explain the concept of frame data and how it applies to SFV over and over.
Seems redundant, right? But in practice, it's easier to find those videos over a singular one, and that single video might not explain it in a way that's easy to digest.
Also, one of the biggest missed opportunities is not riding the coat tails of SFV's success. My timeline was full (and sometimes still is) of people shitting on SFV and telling pro players and others to come to KOF, but like, I'm less likely to play due to someone being overbearing like that. You don't have to say SF, or any other game, is better than KOF, but knowing when and how to offer the suggestion to add another game to a person's roster, not replace, is key.
I've also seem a few popular Twitter boyz excuse themselves for being assholes because "they've already done a lot for their scenes". Dude, newbies don't give a shit, and it's not a good excuse.
Players from any community need to lift themselves and the people of other communities up. A rising tide lifts all boats and all that. The more popular all games get, the bigger the chance someone's gonna try out your favorite too. And if they don't like it, no biggie, but if you were a cool enough dude they will probably recommended it. I feel like GG fans have cut back on the shitting on other groups as of late, and that's getting more SF players to consider playing their game.
That's my theory, anyway.