Playing devil's advocate, it's entirely possible he doesn't know just how controversial an addition Steve would be. If this leaker is telling the truth, then Isaac will not be playable despite how huge and devoted his support group is. Never discount the fact that he's out of touch with anyone who doesn't have Ridley, K. Rool, or yes, even Waluigi-sized fanbases.
Daisy, Chrom, Dark Samus...? Sure, they're Echoes, but they still count for something.
Chrom and Dark Samus were explicitly stated to be in due to requests. Both definitely did not have fanbases anywhere near the size of Ridley or K. Rool, especially after being deconfirmed in
Smash for, and there's no reason to add either purely for marketing at the moment. (Chrom isn't going to appear in the next
Fire Emblem games outside of cameos, and while
Prime 4 is supposedly on the way, we still know absolutely nothing about it.) You could argue that Daisy was chosen to help advertise the
Mario spinoffs, but I feel as though that's a stretch... She was announced by herself to showcase the new Echo classification, not alongside
Super Mario Party, which also debuted at E3, and she's not even very well known among casuals in the same way that Isabelle or any
Pokémon would be.
You have to remember that the team working on the game has a budget, a certain number of people on staff, and a tight deadline. They're going to try their best to please as many people as possible (including the higher ups at Nintendo and any other companies that may be asking for things), but there's only so much that they can do. The only reason we might have half of what we do so far is because Mr. Sakurai is well respected for his work on the series and can get away with pushing back on some requests. The whole Corrin situation proved that even he can't completely escape the executive push, though.
We have no clue what would happen with a new director. They might fold under the pressure to please everyone and not filter out any requests or stop paying attention to details and accuracy, or they might just say "Screw it", and stop listening to fans.
Smash isn't an easy game to make. With Mr. Sakurai we at least know that he has a clear idea of what he wants the game to be, a respect for the characters and their history, and
generally understands what is and is not going to be tolerated by the fans (and companies) without letting them walk all over him.
As far as I'm concerned, Lip and Steve are in completely different situations. No, I'm not particularly fond of the idea of him making the cut, as I'm not a fan of Microsoft,
Minecraft, or Steve, and I'm not a fan of more third-parties getting in before some of the remaining first/second-parties. But I can't pretend that Steve has a direct impact on Lip or the reasons why she may or may not make the cut, or that Sakurai is some horrible, awful person for maybe choosing one but not the other.
I need to stop posting essays, goodness. I haven't even posted half of the ones I've typed.