Have you ever worked in network engineering for an ISP that holds a decent sized chunk of ARIN or RIPE ipv4 IP space, and actually cares about its long term IP space reputation?
There's a big difference between a $5/mo colo/VPS operator that doesn't give a damn, and an ISP that does pay attention when legit "you have customers with abusive traffic" reports reach their network engineering team.
Your comment about not caring about policing badly behaved clients on a network seems like the sort of organization that would land itself on every SMTP RBL in existence.
A hosting company (and Azure and AWS are just the giant corporate evolution of a hosting/colo company) needs to be prepared and have a process to fire a customer for violation of TOS/AUP. It's done all the time. The immense size and callous nature of Microsoft/Azure makes this less likely in the modern era.