The idea is that common knowledge is the tip of the iceberg, and as you go deeper you get more niche and involved. A math iceberg, for example, would start with addition and subtraction, go into exponents, radicals, algebra, then imaginary numbers, series, set theory, then calculus, proofs, theoretical stuff.

The problem is they became popular, so its really just "stuff i wanted to talk about in a particular order". Tier lists are slightly better designed, but people also vastly misinterpret the purpose of those as well; i highly suspect most tier list makers dont even know where S tier comes from