In retrospect, I suppose there's something to be said about DLC's motivation to strengthen ties with business partners.
Capcom and Konami are notably absent from the DLC lineup - they were also two of the most generous contributors to Ultimate's base game content. Perhaps they ended up a bit lower on the picking order because there was little need to build on these relationships. Instead strides were made toward areas less accounted for on the base roster.
1 SEGA (Atlus) character
2-3 Square Enix characters (1 Disney character)
2 Microsoft characters
1 SNK character
1 Namco character
Most of these are representing either a new collaboration, or one that may have been more difficult to work out without DLC. Well, that and Kazuya, but I'm just gonna factor this in as Bandai Namco's reward for all their hard work lmao. Square Enix is clearly the outlier here, likely due to their character / content expenses making these characters more suited for post-game collaboration. Otherwise, we added Microsoft, SNK and debatably Atlus (really just comes down to how you want to look at this one) to our list of collaborators.
All that to say, despite Capcom's vast catalogue of viable and exciting characters I believe that Nintendo felt less compelled to seek out Capcom who had already been so generous and is already such a prominent partner. Compared to Microsoft, whose relationship with Nintendo is quite young or Square Enix who may or may not have been one of the harder companies to convince to allow their one returning character back without the additional DLC tax.
I could see this being one of the reasons, but I don't completely buy it as being the main reason
Considering how Adamant Nintendo was about wanting Dragon Quest, Minecraft, and Tekken in the DLC, even when compared to some of the other DLC, It's weird that at the least, Resident Evil and Monster Hunter, Both Franchises that both Rival and Surpass the Listed Franchises here except Minecraft, did not have a playable spot in DLC, or just the game period
We also know that with Kazuya Mishima Tekken and Steve Minecraft, They were stated to have some challenges when it comes to implementing them into the game, with Tekken going all the way to Smash 4. probably why they had to wait till Fighter Pass 2
Looking at all the franchises and potential characters from Capcom, I think All of them suffered from Implementation issues in terms of a Smash Moveset, for Smash Ultimate. However I think that can be rectified in this next Smash game
So honestly, My theory, and also kind of why I asked about Capcom, is that I could see Capcom making a good brunt of the "Huge Additions" in regards to newcomers of the Next Smash game. You have
-Monster Hunter and Resident Evil Characters as Really the last Huge Japanese Franchises to add to the playable Roster
-Devil May Cry (Dante) and Ace Attorney (Phoenix), which while smaller series, are The Most popular within their niche and also among The Most requested characters right now (And for Phoenix, been requested for awhile)
-Another Street Fighter and Mega Man Character, especially Street Fighter with Chun-Li, which while I've had my doubts in the past about if she can be Implemented properly, I think the fact she's as Iconic as she is is too hard to ignore. Zero is also a character that I think gets decent amount of requests to become playable
-Some of the More Niche picks like Amaterasu, Arthur, and Viewtiful Joe, though I kind of doubt these becoming playable, especially the latter, but the options are there
Since Capcom does have such a easy going attitude when it comes to Crossovers, I could see a scenario where they might be more beneficial for the Next Smash game over trying to force them into DLC for the current Smash game