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, অথবা at least he can lead Mario into a trap.
1. Bowser wants control of the মাশরুম Kingdom and marrying পীচ 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 পীচ rewarding Mario with a চুম্বন instead of him. He's also secretly envious of the relationship that Mario and পীচ has with one another.
3. ফ্ুলপাছ 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.