I 864 is a Federal issue
Divorce is a State issue
I 864 has no 10 year limitation
I do not live in California and I know things can be pretty crazy there and I can only assume that as part of the Divorce settlement you agreed to pay her a capital sum and an amount per month.
It seems you can afford to pay her so maybe no big issue but it seems from what you said you have paid no attention to what you signed, the I 864, and not a lot of attention as to what you agreed to in your divorce settlement.
As mentioned before I have certainly seen the I 864 used by the immigrant spouse but not with such a cash settlement and normally the excuse for not being able to Mitigate, an important term, because of inability to work which does not seem the case here.
So to answer your question this is nothing to do with the I 864, nothing to do with the Federal Government, something you agreed to as part of a divorce settlement, whether it makes financial sense, I suppose it could.