For me, this has been one of the main oddities of 5E's attitude to settings.
They've been peculiarly bad at selling people on what's cool about existing settings. The only two existing-setting books which were unqualifiedly "good" and sold the setting well were Eberron and Wildemount. I don't think it's any coincidence that both were created by the original authors of the setting, not WotC people.
SCAG was a rushed mess, and whilst it roughly serves its purpose, it is definitely not a book that is likely to sell one on how cool/special the FR is, and before anyone gets dismissive about that, I would say that can be done, and that indeed in 1E (Grey Box), 2E (FR Adventures) and 3E (errrr... the main FR book) it was done well. All of those had a kind of magic to them that made the FR feel distinct from "generic fantasy". SCAG is missing that. It's slapped together and slipshod, and lacks that spark of the weird that really enlivens fantasy settings (and that previous FR books did have). I kind of get it, because a lot about 5E's release looks super-rushed, and presumably it was a victim of this, but still.
VRGtR doesn't feel rushed out, but feels like it has to rush, because it doesn't have the page count to do what it's setting out to - which is really to both lay out a new vision of Ravenloft (and one I quite like), whilst also addressing horror in D&D in general, and also whilst creating a new (sadly failed) attempt approach race/species, and on top of all that, jamming in a totally needless and frankly not-very-good and not even that Ravenloft-y adventure (should have been a PDF or free on D&D Beyond). No part of what VRGtR is really done justice except maybe the mediocre adventure, and who knows, if that had more space maybe it'd have been better too. At least VRGtR touches on what makes Ravenloft special, but I really question how many DMs would feel like they should and could run Ravenloft from that. I suspect far more DMs have run Ravenloft thanks to Strahd than VRGtR.
Spelljammer is this whole thing taken to a new level, with equal-lowest page count, and the entire setting, all the new character rules (including several new and weird races and their whole deals!), and a bunch of ship combat rules, together with detailed ship plans, all jammed into 64 pages! A bizarre approach, and again, I don't think it really sells Spelljammer particularly well. Adding to the bizarreness is that part of the Bestiary is stuff that's clearly Dark Sun monsters with serial numbers filed off, and that the adventure is aimed at levels 5-8, and you're supposed to run the free adventure on D&D Beyond first, which is just mind boggling. Absolutely insane stuff. Surely if you're willing to force people to use Beyond to get a usable adventure you should be putting the 5-8 one there? Or putting both, and using those expensive real-book pages to detail the actual y'know, setting.
I don't think there's a lot of point covering the mini-settings attached to campaigns, but I will note it was pretty damn peculiar that Strixhaven went from a pretty edgy and cool setting in MtG to a setting so "comfy" that it makes Harry Potter look like a Cormac McCarthy novel by comparison. I don't think they've really fluffed any of the other MtG settings though MtG fans feel free to correct me.
Quite. Whilst it was clearly well-intentioned, we wouldn't have gotten into this whole mess if it had been better drafted. On the flipside, it might not have been as beneficial to the industry as it's possible that a more corporate approach might have convinced Dancey et al to back down on its generosity. Like a lot of important legal documents of history, it's kind of a mess.
