CG: first I want to say: don't beat yourself up over this. Not the fact that you can't get your father to agree to more care nor the fact that you feel abandoned by your father in this. You care for both your parents, you want to make their situation better: you are a great daughter.
I have hesitated to post this but I will for what it's worth: Is it possible that your father is taking this approach (consciously or unconsciously) because this is what he wants? That is, he wants to predecease your mother? I know this sounds shocking, but we had a a friend, a very good friend whose wife was so close to us that our children called her Grandma Barbara. But she was struck down with AD. And when she got to the point that she had to be placed in a care home he simply decided that all the "I shouldn't eat this, I shouldn't eat that" restrictions that he had because of his heart disease were meaningless. It was, frankly, no holds barred. And he died. And it was his choice. Because he didn't want to live without the woman he loved, wasn't going to go the whole suicide route but was prepared to let nature take its course. As it did.
So maybe, just maybe, your father wants to do everything he can for your mother at whatever cost. Because the alternative is unbearable.
The other thing I have to ask is: have you actually sat him down and said what you have said here? (When I don't know, and that's an additional problem), but have you? I mean been clear in the : I have two parents, one has dementia and is lost to me, but one isn't? And I don't want to lose him. Maybe you have and kudos if you have but it's entirely possible that you haven't spelled it out exactly and clearly (because hey, who wants to). If after that he makes these choices you have to understand that it's not because he loves you less, but because he needs to do this for your mother to the exclusion of all other considerations. Caring for another person tends to make you blinkered: the whole thing is all consuming.
You didn't come over as a petulant child to me. You came over as a caring daughter who wants to salvage what she can. I hope you can, but you may not be able to because while they are your parents they are autonomous people. It's very hard to deal with and you have my sympathy.