How would an OS seed an RNG in the cloud? How would you seed an RNG on a headless server in a VM? What about when that VM is copied, possibly while running, in order to duplicate server functionality? There are vulnerabilities and threats here that your comment does not take into account.

You can use virtio_random.

But really, it's not about operating systems not using RDRAND at all - it's fine to use it as one of the entropy sources; what you don't want to do is use RDRAND directly instead of CPRNG.