They can only use it to run a particular tool related to a piece of MSO software. This may be a relatively short operation, a relatively small part of an agent's activity. Then hundreds of agents can use a single machine with MSO, similarly to how hundreds of CI/CD workers can collectively use a single machine dedicated e.g. to providing secrets and signing binaries.

Thousands of agents could remote into one strong enough machine, or even use DCOM.

Unless you snapshot a VM and run clones of it.

How do you define a single machine?