I ran a team at FAANG where I supported people creating content, including emails, and no matter how many times I explained open tracking was only useful as a trend and not an individual evaluation it just went over people's heads.

Senior leadership wouldn't believe me, kept harassing my team to explain why so and so who said they opened the email didn't have an open event, and why so and so who said they didn't open the email did have an open event.

Authors wouldn't believe me because email open was the highest scoring metric they had. Less than 3% of recipients would land on the page for the publication, but >50% would "open" the email that has a teaser and a call to action to open the webpage. If they had to go off of the click through metrics which are accurate it'd make it sound like they were bad at their job.

So everyone used open rates because it made them feel good. Either that they were writing engaging content, or made them feel like they actually had a handle on who was/was not reading their mail.

No metric would have been better than this metric.

>why so and so who said they didn't open the email did have an open event

This was one of the first known issues when Gmail and others began checking and preloading images/content in emails. It was "triggering" that events/requests to tracking pixels. Eventually folks learned and knew to check the user agent to determine if it was just the mail provider preloading/checking the email content.