Here's the team's description https://nixos.org/community/teams/nixpkgs-core/. They were able to accomplish quite a lot of useful work. The steering committee is a separate organization (https://nixos.org/community/teams/steering-committee/) that contains more people and arguably accomplishes less.

there are two distinct usesn of team/committee/council/etc in the software world, though they often get conflated. one is a formal structure to help with things like coordination and governance when many people are working on something, and it does seem a little silly to have one consist of just two people.

but the other usage is to create an entity, and say "this entity is responsible for so and so problem", and humans then sign up to be part of the entity as a formal indication that they are working on this problem. and in this sense of the word it's perfectly fine for a core team to be two people, and for it to officially disband when those people no longer want to be working on the problem for whatever reason. note that they did try to recruit new people to the effort, and if they had succeeded then the "core team" entity would have provided some sort of continuity to the project despite the original people moving on.