Fair enough. I guess the question becomes what do they think of those old settings once they've had a chance to look at the older material? If they don't like it and like the new stuff, why did it have to have the old names? And if they do like it, why did they make the changes they did?
This doesn't make sense as a question. You posed a false dichotomy, and worse, suggested IP had essentially no value:
I wonder how many of this vast sea of new modern players actually want 5e versions of old settings? Wouldn't they be just as happy with all-new material rather than updates to settings they have no personal knowledge of?
See, that makes zero sense. Why create an entirely new IP, and start over, when you can re-use an existing IP? It reduces the amount of creative work you have to do, which remember, you work at a corporation, you aren't just "an artist", and it means you have a pre-existing fan-base, who are likely hyped about the thing even with the changes, unless they're peculiar (which does happen, admittedly).
You also put off new fans. They aren't more excited because it's a new setting. They're more cautious. More dubious. If it was an existing setting they'd heard of, they'd at least have the seal of approval that a bunch of people used to like this, or it's based on something people used to be into. But you're asking them to get into something entirely new.
This is why WotC has only done two kinds of setting in 5E:
1) Old settings being brought back.
2) MtG settings being brought over.
Why? Because you have an existing IP. The creative work is at least partly done. You may even have art and stuff you can already use, and you certainly have less lore to come up with. Even if the setting is from another game, it already has a fanbase and people who can and will talk about it and its merits.
"But Ruin, you're a monster, a cold-hearted beast, why do you not want creative new settings?"
The thing is, I do. But I know that a big corporation like WotC is extremely unlikely to do more than about 1 per edition (that's been the going rate so far), because they're risky, and an investment. If I want new settings, I'm going to be looking at 3PPs and indie RPG designers. That's where the new and exciting settings will come from.
But the basic idea you've put forth is conceptually unsound. You reuse settings where you can, if you're someone like WotC. New settings are only used where absolutely needed.