They matter when you want to find other people to play with
Exactly, and there again the quality beats the quantity.
Playing a niche old game with old buddies beats high digit player counts with randoms.
I agree completely. Some games and genres really need enough players to ensure queue times aren't awful, and that there are lobbies/games/matches where players of all levels can enjoy themselves.
Battle Royales need big playerbases. Team-based games (like many shooters and MOBAs) benefit from larger playerbases. Fighting games want large playerbases, because it's very frustrating to get a game 6 months after release only to find that it's a Discord fighter, or that the only people playing are absolute killers who destroy you without leaving you any room or time to learn how to improve.
