Big East doesn't have football. Buffalo doesn't have the athletic budget to compete in, say, the AAC. Travel alone would break them.
You have to remember SUNY (the State University of New York system) does not put any value on athletics. They severely limit what coaches can make.
Also most states have only a couple of public universities with one massive flagship. New York State has 65 with 4 university centers (Buffalo, Albany, Binghamton and Stony Brook) designated as flagships. So the student population is spread wide.
When you think about what they have accomplished over the years, getting ranked in football and men's and women's basketball, with all that going against them, it's pretty amazing.
The only way UB takes a big step is if one or a couple of huge donors step up.