You can always let the person in and let them get started (you know, the valuable stuff that actually causes retention), and then prompt them 24 hours later to enter an email address or phone number for account recovery purposes.
Discord basically copied IRC and added voice chat. One didn't need an account for IRC why should they need one on Discord? Maybe to retain their nickname but that's it. And it was just a password, no email no phone number no nothing else.
I really liked the temporary and anarchic nature of IRC. No one was really in control.
The next logical step would have been to make it encrypted and add p2p voice chat via DCC or some other method. SILC tried the former but failed to gain traction, people either stuck with IRC or moved on to AIM and Yahoo Messaneger.