Pajamas

Why do pajamas exist?  We could sleep in the same clothes that we wear that day, but they might feel dirty or uncomfortable.

So why do we have any clothes besides pajamas?  If we trade out jeans or dress pants for pajama pants would it be considerably more comfortable?

What if I start a clothing company making dress shirts, suits, and ties made out of the material in pajama pants?

But then everyone would fall asleep in the board meetings.