I actually wouldn’t say being first generation is an “advantage.” It may be a minor factor in admissions at some places that want to increase diversity and try to help students overcome systemic disadvantage. There are also some scholarships for which first gen students are the only qualified applicants, or for which they have a significant advantage.
But the reason for these things is that colleges recognize that being first generation is actually, on average, a significant disadvantage for getting into, doing well in, and graduating from college. As others have pointed out, first gen students are less likely to do all of those things. Since their parents didn’t go to college, they don’t (on average) have the same kinds of resources at their disposal and knowledgeable, supportive environment at home to help them gain admission to college - and how to navigate through college once they’re there. I was first gen and there’s so many things you don’t know when you’re applying that you can’t get help from your parents on. I didn’t grow up with the expectation that I would go to college (although many first gen students do, so that’s not universal). There were no conversations about applying, about career goals, no college visits before senior year. I didn’t even know how admissions WORKED - I didn’t know what the SATs were or how to do financial aid forms or anything like that. And…neither did my parents. I had to seek out that information on my own, mostly through the Internet. (My HS counselors were a little bit of a help, but since most of the kids in my high school were ALSO first gen, economically disadvantaged, and unlikely to go to college anyway, most of their help was restricted to admissions to local community colleges or maybe a less selective public university in my home state.)*
While first gen doesn’t automatically mean economically disadvantaged, there is a correlation, since high school graduates on average make less money (and are more likely to be unemployed or underemployed) than college graduates. Not all first gens struggle, but they are statistically more likely to.
*This is why I ended up joining CC in the first place! I didn’t find it until my sophomore year in college, but I thought it was great and wanted to help others uncover the information I didn’t find out and learn until I hung out here. Some of the same posters who still post in these forums are folks I learned a lot about admissions and financial aid from back when I was 19 and clueless 