I think you probably need to understand the underpinnings of what Valve accomplished over the past few years to understand why the Frame is useful.
Essentially, it's a Deck strapped to your face. Same OS, same everything, just different hardware platform.
Valve spent the time to revamp SteamOS in order to make it more portable to various devices, which are now launching. Couple that with their efforts on Proton, and you have an entire ecosystem with very little in the way of preventing people from adopting these devices with their ease of use.
Steam Deck was just sort of the appetizer and test launch to gauge interest and build a fully functional hardware development and support vertical in the company, and it was wildly successful. I guarantee (if they can get the price right) that the Frame will sell WAY more units than the awful Vision Pro. I honestly think people might adopt this over buying another version of the Deck if it's comfortable.
Some things I expect to happen with the Frame launch:
- A more expanded integration of Desktop features. If Valve doesn't do it, the community will.
- Virtual screen management
- Theater mode for viewing media
- Virtualized VR input (like steam-input but VR)
- Pairing capabilities for multiplayer
- Half-Life 3 release (not joking)