It's not a reserve currency because the US decided it is, it's a reserve currency because everybody else decided it is. They decided that because they decided it was in their own best interest to trade in and maintain reserves of USD.
But whatever difference it makes is still just a matter of degrees. Countries keep reserves of and trade in currencies other than USD. Some get more benefit than others from this, and they all work to benefit from what advantage they can take from their own positions within their means to do so.
But whatever difference it makes is still just a matter of degrees. Countries keep reserves of and trade in currencies other than USD. Some get more benefit than others from this, and they all work to benefit from what advantage they can take from their own positions within their means to do so.