Whatever IP people temporarily host on a cloud incurs the prior users reputation.

Again, using legitimate traffic to shim network spam is a common counterargument against black listing.

Of the approximate 274000 banned hosts I stare at... many nuisances are from Amazon, Azure, digital ocean, and Hetzner. I am sure Maildrill or Mailchimp does have legitimate use cases, but generally the majority of the traffic suggests otherwise. I am certainly biased in this opinion. =3

Are those hosts using hosted VPS instances, or are they sending through SES? There's a pretty significant difference... FWIW, I get why a lot of VPSes simply block email hosting altogether. It makes it a bit harder for me to find a host for my own small server, but I do understand the pain. Some services are better or worse, and I can imagine at the scale of many cloud hosts, trying to keep the IPs for general hosting out of blocklists would impact the bottom line more than reputational damage for a handful of legit email hosting accounts.

TBF, the demo app referenced in TFA and depending on how many emails you actually send for however many domains may well be a better option for me than my small MTA server.