Why, why, why???

The B is suffering from an acute case of the Whys?
It doesn't matter what I say to him, the response tends to be the same: "Why?"
I don't object to questions per se. To the contrary, I enjoy answering his enquiries, filling in all the gaps in his knowledge. It's one of the reasons that I'm here, after all.
It's the nonsense whys that are getting to me - indeed, getting to us all.
It's the questions that don't mean anything, the questions that can't be answered, the questions that are just questions for questions sake.
Some typical examples from this afternoon include:

The B: "Is that Sainsburys?"
Me: "Yes."
The B: "Why?"

The B: "Is that car red?"
Me: "Yes."
The B: "Why?"

The B: "Is that the road that goes to the shops?"
Me: "Yes."
The B: "Why?"

Me (patience lost): BECAUSE IT IS!!!!!

You can see why, after a while, this starts to get a bit much. Especially when the morning began at 6.20am with the day's first rendition of Baa Baa Black Sheep.
I'm told the whys don't last too long and I'm hoping that proves to be the case.
Mind you, once The B stops, I imagine it'll be time for The G to start.
Why?