We do have our own choice of spending for the bitcoins that we hold. You can treat it as a currency or as a store of value. Andreas don't have to worry about his expenses if he's getting paid in different kinds of fiat. So in that case, that's an advantage to him and he don't have to touch his bitcoin holdings.

I would do the same if I have other source of income and gets paid in cash.

It's impossible that everyone is going to hold, there's a likely that many would hold but it's very impossible that you and me won't be spending some of our bitcoins. And no, it's not a pyramid scheme. Why it should?