Why are iCloud's Servers Silently Rejecting Incoming Email?

My bank recently informed me that an email sent to my iCloud account could not be delivered. It contained an alert to inform me of a credit card purchase. Does anyone know why iCloud's servers would silently reject a message like this, and fail to deliver it to either my inbox or my junk folder? I have received many other emails from the same bank without problems, and I have received similar alert-type emails from other credit card companies.

Historically, Apple has been accused before of such practices. MacWorld reported on this issue way back in 2013: https://www.macworld.com/article/2029570/silent-email-filtering-makes-icloud-an-unreliable-option.html. More recently, iMore has made the same claim: https://forums.imore.com/general-apple-news-discussion/406743-icloud-mail-still-silently-rejecting-mail.html. Last year I made the same complaint, and spent several weeks working thru the issue with Apple Support. Eventually they told me it was another ISP that was at fault. In light of this recent evidence, I am more convinced than ever that Apple is silently blocking emails. Why is it in their interest to do this? Someone, please explain.