Because it's difficult to do. Why SHOULDN'T Iowa be where they are? You think that the University of Iowa is entitled to conference championships every year? There is only one every year and we compete with some excellent institutions, including Wisconsin.
Instead of asking why we aren't Wisconsin, how about asking why Iowa is better than Minnesota? Nebraska? Rutgers? Northwestern? Why is Penn State basketball so lousy?
Y'all are spoiled.
But I will answer the question. Wisconsin has nearly double the population of Iowa. They have a major metro area that is 150% larger than the closest comparison in Iowa, so more in-state recruits. They have a better academic reputation so a scholarship from them is more valuable. They have a larger endowment. They have a larger student body, so more alumni/fans and more donations. They can attract better coaches as a result.
The University of Iowa athletics, including basketball, overachieve by nearly every metric.