This is what it really comes down to. Browsers are built around origins as the major security boundary. When you use a separate origin, safety comes for free.
Trust doesn’t though - discord.com/docs looks legit, as does docs.discord.com - discord-docs.com immediately sets off red flags
And you open another can of worms which is phishing. If you run your marketing campaigns from yourcompany-deals-2025.com don't be surprised when people click yourcompany-login.com links