As the mother of a 2 1/2 year old, I get asked "Why?" about 140 times on a daily basis. Look, don't get me wrong. I'm delighted that she's inquisitive, and wants to know more about the world around her and how it works. But after about the zillionth time, (confession time:) I just want to say, "Because mommy knows everything and you should just take my word for it."
I get that developmentally she's at the age where she just wants to know the reasoning behind things. That's a good thing. But it can wear on your nerves for sure. For the most part, I try to be patient with her and explain how things are working or the reasoning behind what she's asking about. But sometimes, just sometimes, "Why?" makes me want to hide in the corner for about 20 minutes to just chill out.
Oh, and also, I hear "Hey Mommy" about 9,000 times each day.