I can’t speak for OP, but I gave some arguments in my thread when asking to sign up.
In addition to those arguments against the requirement in the first place, I just don’t want to have a Discord account at all. I don’t agree with their policies or their business model of centralizing communities on their platform. It is frustrating enough trying to find communities that don’t use it, and even moreso when it is required to use a completely unrelated service like 2004scape.
The Discord login creates convenience for site admins like you at the cost of the users’ freedom to associate (or not).