I'm not sure it is. It could also just be doing something that D&D can do, that competitors cannot -- go to Ravenloft, go to Sigil, go to Elminster's bachelor pad, etc. If you're trying to double down on iconic branding, MTG settings don't do that yet.
Maybe. Lord knows Archivos/Strixhaven could use more fleshing out.
The D&D versions of these settings are actually very different to varying degrees from the MtG versions.
The second largest city in Akrocoan territory doesn't exist in D&D Theros, the physics are different, the Gods of D&D Theros are more powerful, and the setting is more stable then MtG Theros, there are cities in D&D Theros that don't appear in MtG Theros, D&D Theros has Bards, and Paladins, MtG Theros doesn't, etc..., MOoT also talks about what happens if a Theros demon and Abyss Demon meets up. Its confirmed in be set in the Material Plane and D&D Theros calls the Nyx & Underworld seperate Planes from Theros, in MtG Theros they are different regions of a single Plane.
There are creatures in Ravnica that can Planeshift, etc...
Strixhaven is filled with D&D races, sets the origins of Owlin as the Feywild, has Slaads and other D&D monsters in it, and refers to D&D spells and such. The MtG Strixhaven does none of that.
So these are MtG inspired D&D settings, not MtG settings with some D&D mechanics. There is no reason not to include them.
For alot of younger players of 5e, even ones who never played MtG, D&D Theros and Ravnica as settings have been around alot longer in 5e then most classic D&D settings except FR, Eberron, & Ravenloft sort of, and maybe feel to them like more iconic D&D settings then say Darksun, Planescape, Dragonlance, Spelljammer, etc...