Hi Tamara. 20 years ago after a beginners' Russian class, someone asked me why I was learning Russian. I said I like the women. He said it's the same for him. So I think being interested in the people of a certain culture is one of the main factors for most people. At that time I was also very interested in learning about the different cultures around the world.
Other key factors include pursuit of skill and wisdom. For example, as a martial artist I notice many people learn Chinese to better understand Kung Fu; or Japanese for Ninjutsu & Aikido; or Portuguese for BJJ & Capoeira; etc. And in religion & philosophy people often learn Arabic, Hebrew, Sanskrit, Chinese, Greek, Latin, etc to be more familiar with their favourite scriptures. I've don't study English but I know a lot of people are learning it to enhance their employability (like yourself!) - I don't think many people are learning English to be more familiar with Shakespeare or any other old English literature.
Communication with relatives is another big one - I have a child whose first language is not English so I'm trying to learn her native language to communicate with her better.