Specific business majors don’t necessarily confer good jobs and high salaries. You could major in finance but be terrible at math, end up with a 2.3 GPA and no internships, and have bad job prospects. Or you could major in marketing, but have a great GPA, get interesting internships, and have alumni connections that lead you to a great career.
Also, simple quantity of positions and salary are not enough. You have to actually be i]interested* in the job itself. I love marketing and market research and I’d personally be happier making $65K at a marketing job than $80K at a finance job. It doesn’t matter if there are a million jobs in a field if you don’t want to do any of them!
Finally, majors don’t necessarily draw a straight-line path to jobs - jobs are the ones that have outlooks and salaries, not majors. You could major in accounting but end up in finance; major in marketing but end up in HR; major in general business but end up in public policy. Quantitative skills are always in high demand and careers that demand solid quant skills, like accounting, finance, and operations research, usually have higher salaries. But supply chain management/logistics also is a really solid field to go into.
At both Kelley and UIUC you have the opportunity to take some classes first for a year or two before you declare your business major of choice, so if you can’t decide, the best thing to do is focus on just getting into college. Then once you get there, you can explore a bit and think about the careers that stem from those majors (remembering to think broadly), and choose later.