They use grey listing, black listing, undisclosed mechanisms to degrade self-hostiong intiniatives and yes the goal is to force people to use « cleaning services » like whatever the big company who will read your mail before delivering them. As Cloud-flare is killing the dns, they are killing the decentralized service called mail.
So you can complain, fight, send mail, register your IP to their « anti-spam programs or initiatives » etc and still finish in the spam at the end.
For instance, my domain is hosted at Hetzner® since many years. I’m the only one to send emails since 2001.
Clients I have for many years, hosted at Google® and O365® knowing my mail for all those years have to check their spam box from time to time. Even if I’m in their address books, even if they re-re-re-re-flag me as non-spam … after a while and ramdomly my mails (simple text, no html) are considered evil, bad and stinky by those nice corporations.
Recently it’s Yahoo® who’s choice to check SOA DNS record of (sub)domain −there is no such thing as sub-domain− and simply reject. See a post written a few days ago about it.
This is the way.