The Vault may be getting constant uploads, but you have to look at the Forums and the community themselves. When I say that Brawl modding is "dying", I'm not talking about the Vault. KC-MM is barren and virtually lifeless, with the only section being regularly updated is the Off-Topic section (very rarely do you see any other section get updated). The Brawl modding section on SmashBoards is virtually dead (threads are only updated because there's only people asking for help). The "most active" section of Brawl modding would have to be the Project M modding section on SmashBoards, but even then, it's pretty barren.
Very rarely do you actually see something worthy of being called a "quality mod" published on the Vault, but this isn't anyone's fault. This was something the Vault's always faced (and there's nothing you can do about it without undermining what makes BrawlVault so popular: Its ability to let anyone submit anything, regardless of quality).
If I have to be perfectly honest here, all the mods you listed (except Ridley and maybe Legacy XP/TE) are flat out poorly made. Smash Infinite has got to be the worst example you picked. It's basically the "Meme Mod" for Youtubers to play and make fun of. If the "best" mods you can find recently are just these 7 (in which half of them are mod packs), then your argument just falls flat. Not to mention, you've only been here for about 2 years. You weren't really here when Brawl modding was at its peak (or you might have just been lurking, so who knows?).
Alongside this, virtually every "big name" in Brawl modding has either retired, moved onto Sm4sh modding, or just flat out disappeared. There may be some aspiring modders wanting to make a name for themselves, but I haven't seen anyone new really do anything noteworthy or eye-catching.
Don't let this discourage anyone though. You're more than free to try re-igniting the spark that set off Brawl modding several years ago.
The only thing that could really bring traffic back to this site is if/when the major Forum update happens, which could result in the Sm4sh modders from GameBanana possibly migrating to KC-MM, due to the Vault getting Sm4sh support.
(FYI, the Ridley PSA isn't mine. The one who made it was BaganSmashBros. My edits just fix bugs and overhaul the balancing, but even then, there's still more I need to do).
Yeah, I knew the Ridely PSA wasn't made by you, but BaganSmashBros. username shows up kinda of weird. :/
Even still there are still some good content creators on the vault. Calikingz01 and you yourself are good examples of this. Yeah the examples I listed may not have been the best but they do show that BrawlEx can easily be used to add lots of characters without issues. And Frieza shouldn't be lopped in with the mod packs as "mediocre", it's definitely as good as the Ridely PSA.
I still find Brawl modding more appealing than Sm4sh modding as from what I can tell it's still not quite as advanced.