This scenario doesn't ring true to me. A gamer encountering a setting for the first time will be interested depending on their personal biases. Some gamers love world settings; this has been amply proven over the years and the RPG as a genre probably wouldn't have lasted without such interests. Whether it's a new setting or a returning one doesn't matter to the new player: either way it's new to them.
Some older settings have additional payoffs. A newer player looking through a Forgotten Realms campaign setting book may not know what it is before hand, but there's a high probability of them having moments of "oh, this is where Baldur's Gate comes from..." over and over. Planescape might similarly cause flashes of recognition when they see strange beings they've encountered and learn how they fit into the cosmology.
In general, the question of bringing back old settings is more dependent on veteran players than new ones. Is there enough nostalgia to excite old-timers? Will they rebuy material for an edition update? New players, again, don't see a difference either way. For both groups, the question of whether they buy campaign settings in general matters. I'm sure this latter point is almost all WotC cares about in the end.
Also, in most industries, retreads are considered safer products. Known items repackaged every few years sell reliably. New products are a gamble.
Tbh I love all of those old settings.
Of the stuff new (at least to me as non MtG player) Ravnica did have some interesting themes, although I prefer Eberron.
But Wildemount Theros and what you have not? They sound a bit generic to me, one is a greek style setting, you can do such a things backstory with just reading some of the classic Troja stories and Odysse and there are many more sagas of the Antique e.g. Jason and the Argonautes.
So this one just looks to me like a historic campaign modded with some custom stuff.
The Wildemount thing does not let me recognize something that lets it stand out. see:
- Dragonlance had dragonlances and a lot of dragons and a very epic story like LotR
- Ravenloft had all of the nice grim mods to the game back then and real good RP stuff
- Planescape was crazy and so fresh with philosophies like believing in something strong enough makes it real or the totally different layout of sigil and supercreative use of teleport portals and keys.
- Darksun had all that you would expect from a savage setting plus many stone to bronze age cultures and Psionics which could turn your super tough Halfgiant tank into the enemies pawn in a second.
I take this one ten times over Theros.
- Forgotten realms, the eye of the beholder series CRPG which really brought me into pen and paper D&D, the wild magic and dead magic zones, the mythals, the underdark (yes guys these were the prominent features of FR back then, believe it or not)
- Eberron has me as a supporter the instance I started playing DDO ( from 2006 to 2008 and from 2013 till now, best Hardcore D&D MMorpg) Warforged the magetech/steampunk atmosphere
So all of these have some vibe something that draws you in, every new setting has to compete heavy to get a comparable swag. It is not enough to simply have a setting with some new races or without humans or races fulfilling different stereotypes. Also architecture, techlevel, pantheons, it all has been there and better, it simply is not enough to get me excited just to refluff a bit and call it a new setting.
With this in mind I rather want them to continue FR, they cannot really do it wrong because of the diversity of FR. It is better they do work on a recognized setting instead on new stuff imho.