i think the reason why they want to learn is that chinese is sooooo cool, haha

汉字很漂亮。

like many people want to learn English.Language is a tool to connect others.

There are lots of answers for your question,which start right from building a persons career to looking for a GF.
You just answered a part of a question.Below i will answer rest of the missed answers for your question.
1> If a foreigner is working in China,learning chinese language for him/her will boost career and bring him/her close to his/her collegues.Its a tool for winning peoples mind and getting efficient work done.
2> Language is a skill which remain through out a person's life.Its a treasure.
3> Tomorrow if a person go back to his/her country,this person will be taking chinese language which can be a valuable asset to share & teach own country mates.
4> Its a pleasure to learn one ancient language like chinese,which is followed in countries like Singapore , Malaysia,Taiwan & HK.And let me tell you there are some philipinos coming from Chinese descent who speak chinese.

personally I started learning Chinese for absolutely no reason! lol
I finished uni in England and decided to take a year break. I decided to come to China as I had a friend from Shanghai in uni in London.
Enrolled in SISU and learnt Chinese for 10months. After that I decided I would stay in China.
Now I have been here for 4years and translate! Haha, I have no hidden objectives.

hem
really i started to love china when i saw a movie in the tv. i thought that it was chinese but then i knew that it was corean.
and i have a freind who ove china ( culture, people, history and acupunctur), he told me some things about them and then i became intersted too. i have searched on the net an then by chance i found italki. i like it because it has different sounds, not like he western 's one; short sounds that make it really different. not like( congratulation, agricultur, knowledge). that short sound smake me interested.

the same as why more and more people want to learn English and Japanese
maybe they would to fine a foreigner girl/boy friend?
of course no!!!!

I am learning Chinese for two reasons: (1) for career advancement, as I foresee that our country would be exporting talents to China in the near future and having a grasp of the Chinese language is an advantage, and (2) for fun, because I want to read Chinese novels.

A long, long way to go!

i just like to learn chinese because it's cute and i can use it if i work in china

we want to learn chinese cuz chines people dont understand english so its very hard for us to stay in china with out chinese not for making gf