A big reason for people having tons of unread emails is a poor signal-to-noise ratio of incoming email. When there are multiple useless mailing lists, notifications sent in email, emails where all the important information is in the subject line, etc, and a tiny fraction of actually important emails that require a response, it's much easier to lose track of what's going on. It's even easier to lose track if there are other commonly-used communication mechanisms for important things (e.g. Slack or meetings). That's not to say that 200k unread emails is acceptable, it's well worth periodically deleting all the crap, but the "red bubble" notification count is useless if too much of email is noise.