Most cloud providers have availability regions and zones, with some services specifically having multi-region/multi-zone options (usually with extra cost). Is there any provider that hides this?

They shouldn't advertise as 'cloud' then. I know it's a marketing buzzword and no guarantee for redundancy or anything, but still.

a 'cloud' provider should have, at the very least, multiple redundant datacenters in one availability zone.

Literally no cloud does that. An availability zone is pretty much by definition a single point of failure, and you need to architect accordingly.

That's why you have multiple availability zones. Those are the physically separate locations that you have visibility into and can spread your infrastructure across. Having multiple data centers in a single availability without visibility into where your systems are is fairly useless. And if you do have visibility then you now simply have more availability zones so why bother renaming things.