Running the hypervisors built in to unraid or truenas are certainly options but proxmox/VMware are just easier. If you’re learning about virtualization, you’re going to find a lot more resources for proxmox/VMware. Conversely the storage capabilities of proxmox/VMware are either severely limited in the case of VMware or just not particularly user friendly for proxmox. By virtualizing your storage OS you can get the best of both worlds for some situations. Sure, there are situations where it’s a bad idea but if you’ve only got one machine and it has plenty of resources it can be very effective.
Heck even if the main function for the NAS is just windows shares, that full blown storage OS is going to give you redundancy, snapshots, and replication. I’d say those are pretty important even for Windows shares.
Think of it as kindling for a fire. It’s not going to fuel the platform long term but it’s probably appealing to a lot of folks right now. Hopefully it will spur engagement which will then spread to other more interesting and sustainable topics.