I suspect that the wording of your title, “Scholarship Policy” might be adding to your confusion. At most colleges, there are two different types of aid: 1) merit aid, aka scholarships, and 2) financial aid, aka need-based aid. At some of the schools with the lowest admit rates, they may offer very little or no merit aid and only offer need-based aid.
So, for instance, if a school costs $80,000 but they give a $50,000 scholarship (aka, merit aid) then the family’s portion is $30,000, and any outside scholarships earned are likely to reduce that $30,000 by the amount of the outside scholarship. The scholarship is generally given to attract students who otherwise might choose to go elsewhere.
In contrast, if a school costs $80,000 and they determine that your family can only pay $30k (and they indicate that they meet full need), they might give you a financial aid package of $50k with the expectation that your family pays $30k. If you get outside scholarships, most colleges will reduce the financial aid (i.e. need-based) package, so the outside scholarships (beyond loans and work-study) are decreasing the financial burden on the college, not on the student. So in the above example, if you earned $60k in outside scholarships for an $80k school that determined your family could contribute $30k, you would then receive no money from the school and your family would pay $20k (i.e. $80k-$60k).
Sometimes one will read a news story where it is reported that a student got a full ride scholarship to Harvard or Stanford or similar. What the reporter is actually disclosing is that the family had so much need that the university covered the entire cost of the student’s education. Schools like these (and at BC) have so many incredible students that any/all of their students could be deemed as “worthy” of a scholarship. These institutions have thus decided to offer little/no merit aid and instead focus on need-based aid to make the school more affordable for the students they invite to attend. But as a consequence, outside scholarships generally end up benefiting the university more than the students.