Well, it turns out that Google randomly groups some of these messages in a single thread. And yet this thread looks identical to a single message. So I click on the thread, read the first message, see the email footer and go back to Inbox to read the next one. This marks the entire thread read even though I didn't actually read the subsequent messages. So I never come around to read them.
I completely believe that most users will not read any email in the thread beyond the first one, because there's absolutely no indication there's more stuff to read.
There's still a lot of improvements for mail UX. I don't expect google will be the one to make them, but maybe they'll copy the other people who do.
IMO, gmail is in the wrong here. If the message id is not in the References or the In-Reply-To header, it's a new conversation.
EDIT: Hmmm. It appears that I CAN change that.
Recurring messages having the same title is an absurdly common pattern. Almost every service that has ever sent me a password reset email has used the same exact subject. Same goes for things like shipment notifications, order confirmations, purchase confirmations from PayPal, etc. So given this, it's kind of absurd that a MUA would be designed in a way that buries all those emails, isn't it?
Let's assume that it really is intentional that gmail buries all those messages, on some presumption that they aren't important or on a 'well fuck you, change it then' basis. There definitely are services out there that append random numbers to the end of automated emails. I always assumed this was to make it easy to sort threads by unique id, i.e. customer service systems - so maybe they've been applying an undocumented Gmail Best Practice this whole time. Assuming that this is a good feature implemented correctly, why does unread/read status not work right? If I click into a 50 email long unread thread and then click back why is it INSTANTLY marked read? How is that a useful behavior that would seem intended to anyone? Non-threaded views like in Outlook do not work this way. The common 'reply up top, history at bottom' email formatting also avoids this problem, which you'd think the gmail frontend designers would be aware of.
I would argue that both behaviors are either a bug or user-hostile design. Calling it a bug is generous to the designers because it assumes goodwill and just views it as an oversight or error in a very complex system. I'd personally be inclined to call it bad design, because Gmail is full of bad design, but there's nothing weird or bad about a user calling it a bug!
A $187M figure is super realistic to me given how often I see this particular problem affect me. It literally happens daily. Naturally, I learned years ago that gmail does this and got used to having to dig through my email history to find out where a notification went, but it's still a bad behavior and it still catches me unaware sometimes. I've missed important emails this way.
The difficulty of maintaining Inbox Zero in 2019 also combines poorly with these behaviors - when a notification for password reset or whatever gets threaded in to an email with an old date on it, it can make it harder for your brain to process what just happened.
Essentially Gmail (and other mail services) put messages from the same sender with the same subject into a Conversation View. Users are confused by it, and clicking the oldest password reset link (expired) rather than the newest.
Claims that users being unable to reset their passwords costs Expedia $187M.