It's tactical.
Forget Bupsi for now.
Simon must have felt that nobody is as good as Anton so why put a "second or third place" in.
So, Max goes in due to his performance vocally. Then it's a case of, of the rest, who is most different. He's fixed on pitting his potential winner and then added variety.
I'm not saying I like it or agree with the decision. But that is the employed logic. No point raging.
Rather than say how can he put Bupsi through over Jennifer/Ebru. The quandary should be, is Anton (or Max) worth leaving out so Jennifer/Ebru can have a place.