I’ve just never personally voted using RCV on a ballot that requires you to rank that many candidates for a valid ballot. That seems unnecessary.

Several implementations of it in Australia are full preferential, and require ranking all candidates (and there's a kind of hybrid optional implementation in the federal senate where there is a minimum but you can rank as many as you want). The NYC one is still optional preferential actually, which is in my view a bad system because people get tricked into "just voting 1" and their vote consequently has less power to influence the result.