Yes, because the live chat that happens on IRC is meant to be ephemeral. It's a place where you go to hang out with people, shoot the shit, or ask off-the-cuff things. Most IRC moderators have a no-logging policy because it's supposed to be a shared space that people "move into and out of".
Email is where official business happens. That's where debug logs are pasted, and people can reply on a point-by-point basis, with quotes, references, and attachments. It's meant to be high quality/detail and searchable. That's why mailing lists have archives.
When IRC and email aren't separate, you get Slack and Discord -- places that don't do either off-the-cuff chat, or searchable documentation, particularly well.
Is there a compelling reason for those to be separate, beyond "we've always done it this way"?