Because she was so beautiful

"Because you are insanely beautiful mom! I mean I seen you changing and I couldn't help myself. You have to be the most beautiful woman in the village... maybe even the world!" Naruto spoke what he truly meant, these weren't just words of flattery or trying to stay out of trouble he genuinely though about that.

To say Kushina was floored would be an understatement, as she was completely gobsmacked at the revelation that her son thought of her that way, though she couldn't help but get a little touched, and turned on at hearing that. "I well uh... that is a lot to take in but... I suppose that is rather sweet and... wow I don't know how to respond."

Kushina didn't really know how to respond to that, she didn't think he son could possibly feel that way about here, yet here they bother were. "I know that its wrong but... I can't help it you are just so amazing!" The whole time Naruto hadn't stopped jerking off his cock, letting Kushina get a very good look at every single inch of it as his hand went up and down the immense length.

"Well... it is really sweet and I guess you are a growing boy so its own natural that you would act like this." Of course that was just what she told herself, her son was a grown man now not a kid, he had a cock that put all others that she had seen to shame and after catching him training she knew that he was really well built.

"Thanks...If you want I can leave... I know this is a little awkward." Naruto offered to leave, even if he didn't really want to. He loved his mother and if she didn't want him here and doing this then he would go.