Why should you want to be Bilingual?
I think that you should want to be able to speak many different languages.
Many people in many areas in the world are bi-lingual or tri-lingual, one language at home, another one at school or perhaps at the market.
It's being monolingual that's the oddity.
learning a foreign language is the entry gate to learning about ,and getting to know the various cultures of people who speak that language, consequently, expanding our horizon and teaching us more about our own culture which is the core of what we are. The more languages we learn and speak, the more we know about ourselves. To me personally, next to many other reasons, this is the most valuable aspect of learning foreign langues.
If I may add, it's not just learning a "foreign" language it's learning a second language.
It could be a minority language for instance.
Each language offers you a different perspective into the world.
some people think it is too hard to learn more then 2 languages. so they don't
I think it opens up many possibilities job wise. The company I work for here in the US is Japanese based and they've stated multiple times an easy way to move up the company ladder is to be bilingual in English and Japanese.
Most of us are well beyond the stage of brain plasticity that would allow us to be come truly bilingual, so wanting or not wanting is a little beside the point.
That said, there are many established benefits to learning additional languages. Alongside the ones other people have mentioned, learning a language can help stave off dementia as you grow older: https://www.newscientist.com/article/dn24537-learn-another-language-to-delay-three-dementias.