It comes down to character and personality.
Melania fits Trump in a way Ivana and Marla didn’t.
The woman isn’t a feminist and prefers not to be the co-wife.
I think that’s the way The Donald likes it.
Also I always got the impression that Ivana was trying to be a controlled freak with Donald. That is why I think he just had enough of her and fell with Marla whom I don’t think he loved her. I believe he finally found his true soulmate and that is with Melania.
I read an article where he discussed his wives and he said that it was a mistake for Ivana to become involved in the business because there was no relief from it when he came home. I can understand that...from experience. He said Marla was a really spiritual person (?) and that they should have just been friends. Melania is his soul mate - they both think that.
So the man loves beauty and married a spectacular woman - I don’t begrudge him that. Probably most men would if they could.