It being free and open is exactly what the big providers can't stand and why they are coming up with ever more "standards" that are complex to configure as well as "reputation" scores that are hard for small senders to clear.
Also why they do non-standard stuff like accepting mail but then simply not delivering it, rather than bouncing it.
DMARC is not hard.
"Reputation scores" and blacklists / greylists started in late 1990s / early 2000s as multiple grassroots efforts when spam started to overwhelm systems. Gmail did not exist, outlook.com did not exist, it was easy and expected to run your own SMTP (which I did). And it was very unpleasant.
DMARC appeared 10 if not 15 years ago. There's no reason for a sane MTA configuration not to have it.
Microsoft has provided free email addresses to the public for decades.