I am going to point out now that I've been running my own mailserver for 15+ years
And I can't send mail to people with Apple or Google accounts. Why? Well, I'm not a known corporate entity. They whitelist email to known large businesses, an unrecognized IP gets blocked directly.
So y'know, yeah. Globally recognized protocol, got all the SPF/DKIM/DMARC/etc, but when it comes down to it, once big business gets a majority of an open protocol? They will devour it
