Probably because there is literally precedence for what is "currently relevant" getting skipped over for what is upcoming for Pokémon even as early as Brawl.
Brawl's roster was drafted on July 7th, 2005. Diamond and Pearl wouldn't be out until September 28th, 2006. We still got
over anything from Ruby and Sapphire.
Smash For's roster was drafted on April 26th, 2012. X and Y wouldn't be out until October 12th, 2013. We still got
over anything from Black and White.
Ultimate's roster was drafted on December 15th, 2015. Sun and Moon wouldn't be out until November 18th, 2016. We still got
over something additional from X and Y or even OmegaRuby and AlphaSapphire since those were released by then.
With that in mind, is it any wonder people feel Scarlet and Violet missed the mark? The roster would have had to be drafted at some point between October 5, 2021 and November 18, 2022 for Scarlet and Violet to even have a chance.
As for Fire Emblem? Similar deal. We got
as DLC to promote an upcoming international release of Fates and
was specifically chosen as DLC before Three Houses was released even if they'd be released after.
And we know from Sakurai's words himself that the likes of
and
would have been in jeopardy if Awakening released half a year earlier or later than it did. So for Engage to have a shot at the main roster we'd have to assume it dropped in the right time frame from when the hypothetical new Smash got its roster settled.
So yeah, until we know that a new Smash is for sure on the way and had been worked on since Sora was revealed at the earliest, it's better to assume Scarlet and Violet as well as Engage are **** outta luck.