Interesting. An obvious motive is they can no longer afford their American lifestyle and no longer have any supporters or income streams there. It was always likely H would want to return to the familiar UK and get his bills paid when the freedom fantasy failed. I wonder if someone took him aside and gave him some pointed advice about Californian divorce law and the significance of the 10-year deadline, especially re the kids.
When not in thrall to M, H has always had these royal trump cards to play. I can't imagine him not getting restless about his older wife and looking to younger women, maybe M won't mind if there's a good lifestyle deal for her, she has to compromise somewhere to maintain status, she hasn't any of her own.
The pull to have access to some of his former life must be strong for H, he must be like a fish out of water in Montecito. Also he clearly didn't really want his kids to go barefoot to school in California.
I hope the Palace manage to keep a lid on them, I expect the promise of funding will be the key to that. Funding from their family, not British taxpayers. Unless H sobers up and they genuinely behave themselves, bad press will continue to follow H&M, it's to be hoped no fool decides tries to make them 'working royals'. I'm not a royalist but I feel on a human level for KC3 and hope he gets some peace after this.