That's probably because of your upbringing and your surroundings. When English is your native language, and all the input you get (books, tv, music, internet) is in English, there's little incentive to learn more languages.
For a majority of the people on this planet, this isn't the case.
It's extremely circumstance based. I have countless relatives that are tri- or quadri-lingual (or more), merely because they have different cultures in their background and/or were forced to immigrate. Those that are uni- or bilingual simply were lucky enough (or stuck enough) that they didn't move much. And I don't think there's any particular astonishing knack for languages needed to explain this.
Additionally, if you're exposed to a new language early in life, it becomes much easier to learn new languages in the future. And being immersed in it forces you to learn, as your survival depends on it.
So, incredibly impressive? Nah. Mind you, if someone is legitimately a fast language learner, given that I am not at all, it does impress me, especially if they truly master it and can think in that language.
It isn't. I'm Dutch, and had to learn Dutch (obviously), English, French and German. And so did all the other people I know. People who attended gymnasium also had to learn ancient Greek and Latin.