People attend college for several different reasons.
They want to be educated - a diploma could make us have more self-confidence, thereby opening the doors for us to have relatively happier and easier life. There are some people that just get education just because they want to feel and know they are educated.
Have recognition - One might have enough knowledge or expertise in a particular work area but during a job interview, they could still need a diploma to prove this
Get new skills- Many jobs will require particular skills most of which probably are not possible or not that easy to learn on our own. University or college education would easily provide the necessary knowledge and training for us to get new skills
Learn new things
Get to know new people - addition to these, for some people, the university life could be more attractive than the education they get. They could easily find opportunity to socialize and make new friends
Better life conditions in their future life
To get a job - Many people are simply after a diploma just to make it easier to find new jobs.
A better person in life - Moreover, For some people, especially the students who get their education somewhere away from their families and homes, university education might help them learn how to live on their own and stand on their own feet. The hardships they face during their university years are challenges that teach them a lot about life and help them get to know themselves much better.