Back when I was a teen I used to fraud people and scam ebay sellers through paypal. If I were to somehow gain access to an email (via RAT, Cookie hijacking), one of the easiest ways to recover a password was to look for a provider that sent out a plaintext password. Chances are the unfortunate target used the same password on every site (or if it was lowercase and alpha, that password + "1").

That would grant continued access to the email, and other sites that took protection a little more seriously like Paypal and Bank Logins (you can't reset a Paypal password with just an email, and if you could, such an action would make Paypal fraud detection software go nuts).

"Back when I was a teen I used to fraud people and scam ebay sellers through paypal".

Cool!

If the password is in the email in cleartext, you don't need an active login for their email. All you need to do is be looking over their shoulder in the cafe, once, when they bring up the email on their iPad.

Given an uncertain amount of time. Your process requires access to their email account while you go through and reset all their passwords. Whereas if the passwords are in plaintext, you can download all their email and get access at your leisure.