Speaking from being very early on the train for Discord, it also had an extremely solid userbase right from the start because much of the early pre-marketing pull into it was for raid groups in the then-new Final Fantasy XIV: A Realm Reborn. People really needed a chat client to coordinate a big number of players and it was totally free, functional, and new on the scene. It spread a ton in the community and the people working on it were players as well from what I remember, though it's been a long time. So as the game grew in popularity, and everyone who was in a large group was starting to use Discord more, it cemented friend groups that formed in the increasingly popular game along with the Heavensward release and helped solidify a foundation in the gaming community imo.