There has to be a very niche market for people who want ChromeOS on their device but do not have the technical know-how to do so, or without a device that can flash an iso.
I guess for $3 it's not really a cash-grab or anything. Kinda nice to see vendor-supported live USBs honestly
It kind of makes sense for it to be a partnership with Back Market, which also sells used hardware.
That way, the ChromeOS USB key can be an add on to the purchase of some old laptop that can barely run Windows anymore.
I'd say the majority of people don't know how to install an OS on a device and having the ability to run Chrome on what is likely e-waste is a good thing.