The nuance here is that the word "kind" really carries a lot in that statement. Men are not very picky, so finding some lofty "reason" or list of reasons for why you are with a woman isn't always easy. A lot of the time, it's not some crazy calculation like "wealth, social status, height, how he makes me feel like a princess", but rather you get attached to a woman because of her looks and then she makes you feel wanted. If she makes you comfortable to be around her, that bond grows. For Inuyama, her kindness is what made him be able to grow that bond.
Once it grows, the attachment is hard to put into words. Can you explain why you love your mother or your father? Is it really "because they brought you into this world and raised you." Does that really "explain" your love? In my opinion, no, that sentence itself feels pretty meaningless compared to the love that I feel. It's a bond; it just is.