People conflate notability with recency, rather than looking at general impact, all whilst deluding themselves into thinking the only audience that matters are little kids and that anything that has a recent successful game is automatically going to be more appealing than characters with a lack of recent appearance. Despite
the average age of a Nintendo gamer being 31 years old according to a 2014 ESA study as well as
Switch owners being overwhelmingly in in their 20s/30s, people genuinely thought a character like K. Rool would be "too obscure" to be popular among the silent majority just because he hasn't had a recent game appearance (even ignoring the fact that the games featuring him gets re-released for recent consoles, most recent example being DKC which was part of the +5 million selling SNES mini). People let Smash's agenda dictate their opinion of what is and what isn't "worthy" or "important"
At any rate, people grossly exaggerate how much recency actually factors into potential appeal, especially since practically all the Nintendo characters who are insanely iconic enough to be appealing based purely off recognition are already in at this point since the Inklings were confirmed. Even disregarding their huge impact on their respective franchises, characters like K. Rool and Ridley were naturally going to have a huge appeal within Smash even if they weren't all that well-known in the grand scale of things just because of how much they would feel like a fresh breath of air, even disregarding their established support and how well-received they are within their series fanbase. In contrast, despite being from a recent game that sold much better than any recent Metroid game, a character like, say, Rex wouldn't have the same type of potential appeal that K. Rool and Ridley has mainly because regardless of how different he would be from Shulk, he wouldn't be
perceived to be as a particularly diverse, hype or interesting just because of his visual similarities to Shulk.