Bowser's main goal is to defeat Mario. He knows that if he kidnaps Princess Peach, Mario will do all he can to save her and might die in the process, または at least he can lead Mario into a trap.
1. Bowser wants control of the キノコ Kingdom and marrying 桃, ピーチ would give him the power to do it.
2. Bowser has a crush on her, which was first revealed in Super Mario RPG when he got jealous of 桃, ピーチ rewarding Mario with a キッス instead of him. He's also secretly envious of the relationship that Mario and 桃, ピーチ has with one another.
3. デイジー is a tomboy and is less prone to being kidnapped. However, she was kidnapped in Super Mario Land. But still, I don't see a reason why Bowser would WANT to go after Daisy.