Well did TSR have the analysis tools and do the researchto know what themes and tones were popular with which audiences? Or did they shoot out a lot of settings because they had to and thought they were cool.
Quite frankly, the designers in WOTC has the tools and skills to make a new setting that sells well. The fact that they haven't yet is proof that milking nostalgia was a core goal by those in charge of strategy.
Thing is, the company goals are so different now than they were before that it's really hard to compare.
Since the release of 5e, WotC has pursued a pretty clear policy - every release is a major event. So, they bank on having only a couple of releases a year, but, they are going to do everything in their power to make sure that those releases are successful. And, I'd say that this policy has been an unbelievable success.
Now, as far as milking nostalgia goes, sure, they certainly did that. But, there's been stuff that's been new too. Candlekeep Mysteries, Dragon Heist, now Strixhaven and soon Radiant Citadel. These are all pretty original stuff. So, they aren't just banging the nostalgia drum.
Given that the 50th is coming up, I really don't think we're going to see a really original setting. Although, I might be totally wrong. Maybe they'll use the 50th to try to really hammer a new setting down. I doubt it, but, it could happen.
Honestly? I think they'll do a sort of mini-playtest period to create a new setting. We'll get a truly original setting when you start seeing a series of Unearthed Arcana's teasing features of the new setting in order to drive up hype. But, considering we're getting Dragonlance and then Spelljammer? Naw, we're not going to see a completely new setting for a while. If you want a new setting, much better to go 3rd party for that.