It is about winning and losing. I athletic program mandates a huge financial commitment on the college's part. Thus, for it's teams to be competitive nationally a college needs to fully fund the programs, which can requires millions of dollars. It means athletic scholarships, new facilities, a full-time coaching staff, expense paid training trips, interim housing costs during vacation breaks, team practice and competition gear, and corporate sponsorships. Each college decides which sports it will fully fund.
Most colleges lack the resources to fully fund all their programs.
Since each college determines it's focus, they may fully fund certain teams and partially fund others. Very few men's soccer programs in the country are fully funded. Now, with Title IX, there are more women's teams sponsored, but not necessarily fully funded. Very few teams offer full scholarships to incoming freshman. College coaches can offer partial scholarships, thus signing two or three players for the price of one.