Sample size calculators compute variance, not bias. If a survey is not conducted properly, then increasing the sample size will still give you the wrong answer, but just with more apparent precision.
A survey of students is going to be problematic because student populations are different at each college, and students don’t have any basis for comparing their college to another college. Not to mention that students are often making their judgments on trivial issues, rather than those that really matter. And those are just the problems if we took a random sampling. Web sites like Niche have the additional problem of soliciting responses from students who often have some agenda to fulfill by making a comment.
Look at all of the incorrect poll results before the November 2016 election – the sample sizes were sufficiently large, and a lot of careful thought went into planning these professional surveys, but there was still an inherent bias in how they were conducted.