Couldn't have much good in season 6 so life had to be absurdly bad...and obstacles (including all the Scoobies) had to be tweaked or removed so that the Spuffy arc could happen.
While I could add more to my previous idea, I can add that Giles would be afraid of what other Watchers would do with Dawn (and they'd surely run their own magical tests on her, just to be on the safe side even if they didn't know she was the Key), and also that it would probably look weird to being a bureaucratic nightmare for a foreigner to adopt the girl even if he didn't leave the country. And in this case the system would be sure to alert Hank in that case, though all things considered in season 6, Hank may have very well been the best choice--and get Dawn far away from the Hellmouth in the process, the town that made the worst parts of DC look like Mayberry with no one saying boo about it even with Buffy present). Despite this, I still think he's the best choice character wise if restricted to the Scoobies.
It's unclear how Angel in LA owned anything as he technically didn't exist within the system...though I guess he had something. It would still be dangerous (might as well stay in Sunnydale). Though I will say I don't see Angel kicking Dawn out as he did Connor for multiple reasons. One, Dawn doesn't have the toughness and power of Connor who grew up in a world far worse than our own (IOW, he shouldn't be thought of, or written as, some soft middle class kid in the USA). Two, Dawn wouldn't have been bold enough to take part in such a plot as Connor did. And on the meta-level, the writers subconsciously thought of females as weak and vulnerable (among other things) and that showed in their dialog and character arcs (where it took deliberate resolve to write a female character as anything else--even Buffy suffered under these biases when it was tangential to the main story they're writing about), which means it would just not do to have Angel to kick the little girl out onto the streets. But still, there was danger aplenty (and I'd be fascinated to see how Jasmine and Dawn reacted to each other). (And I'm even less thrilled with the other members of AI getting guardianship over her, at least if they remain in LA.)
As for Xander & Anya (not counting anything in the comics that I consider AU anyway), their place was smaller, and I can see the fandom (many of whom forget that kids aren't as ignorant and fragile as they think of them, and given what I recall of growing up, I think many must've blanked out much of their own childhoods) would not like to see her exposed to the likely talk and sexual antics of the pair (which she'd probably hear, though it would amuse me if Dawn learned to play the TV really loud, and occasionally make some comment in front of the Scoobies, one that would likely to followed up by Anya adding something, that caused Xander to squirm) so that would be out (unless they just want to pretend Xander and Anya's room is in another dimension, IOW, pretend Xander and Anya are, at the very least, very discrete, and what's one more character revision?). As for me personally, I just don't see Anya or Xander as parental figures willing and able to put their foot down with Dawn (though Xander would otherwise be responsible), or at least easily distracted or tricked if they do.
And one more problem that is a strike against everyone but Willow and Tara: if Dawn moves then that draws attention. Pretending that season 6 approaches realistic, then at the very least they'd have to PRETEND Dawn lived in the Summers house (and she'd probably go there on her own anyway) as otherwise that has to be noted on school records and the like, and if Buffy isn't around to give her signature as well as fill out other paperwork involved (like say a lease which would likely require selling the house, etc) in the move (the Buffybot wasn't up to that task) then that could cause problems right away (and if Scoobies got killed on patrol, she was technically safe from vampires in her own home--that is, IF it still counted given that the legal owners and guardians were dead), and that's in spite of stupid cops and Sunnydale Syndrome. Granted, Willow could use magic and we can pretend it doesn't have consequences beyond Tara whining about it, but it still seems like a lot of risk to move her somewhere else.
But Willow was increasingly reckless and hubristic, while Tara didn't strike me as someone who could do more than wag her finger (even if Tara could keep from shriveling up should Dawn say something mean because Tara put her foot down, she might still find herself drowning as an empath in Dawn's intense feelings). Still, there's plenty worse out there, and I can see the situation being as it is at the start of season 6 with Dawn living in the Summers home under the two witches.
I'm still wanting to know more of Hank who was far from the Hellmouth, though Dawn would have issues of "not being real" so that her father's love wasn't real--and his love seems selfish and fickle which would exacerbate that feeling--whereas the Scoobies knew what Dawn was and accepted her anyway. Perhaps that alone made Hank unsuitable for Dawn, despite living far away from the Hellmouth (and there's really not much else to know about him).
