The 3E Draconomicon included a lot of player options. So it's just about which norm they're following.Well, I don't really agree that Strixhaven actually fits the evidence that much (beyond owlfolk, I don't think the UA actually matches Strixhaven much).
Right now my going theory is that this UA is for a July book that combines the dragon-themed and fey-themed UA into a Volo's/Mordenkainen's style monster book. The biggest break from the norm here would be that it would contain some class options, but I find that an easy jump to make if they are on-theme.
It's certainly possible this is a monster book, but the combination of dragons and faeries doesn't feel like a natural one to me.
I understand -- and agree with -- the reasons it's unlikely to be Strixhaven, but couldn't this be Eldraine? Arthurian setting with faeries and dragons?