^ this. a single long session may use 20 subagents, each of which need their own VM, on top of the parent agent's VM, all of which may need separate security credentials, isolation, in addition to the spinup time, and resources used. each user might do 100 sessions a week. so that's 2,000 VMs per week per user. each regular VM takes, let's say, 10s to boot up. that's 5.5 hours per week just waiting for VMs to start (for a single user).
then there's the disk iops used for spinning up all these VMs (loading and booting a whole distro), the security attack vectors of an entire VM vs microVM, the maintenance of the images, the hypervisor abstraction to handle all this automation, ssh for the agent to run in the VM, etc.
compared to mounting an extracted container image to a folder, starting a microVM kernel with folder mount, with specific credentials attached. minimum memory and CPU allocated, minimum possible system resource use, fastest operation, least maintenance. you get more time, more resources, more security.
(micro VMs do provide better security isolation. they have kernels with fewer built-in vulnerabilities, fewer hardware drivers to exploit, a more locked-down network, and they lack a full OS's applications and filesystem permissions to exploit)