"up to date" implies that fixes are being identified, developed, and distributed. If your wifi card has some flaw, and intel fixes it, and google distributes the fix then your device is "up to date". If you don't care about this property then you also don't care that a Chromebook only gets updates for 7 years. It is, after all, not going to just switch itself off at the end of the support term.
1. Intel spectre/CVE?
2. Note that these old devices have no support from Wayland as intel does not provide drivers
3. These were introductory chromebooks and I am sure OEMs will be annoyed if they are unlimited updates. (or they may be have contracts)
4. Even if google kepps them away from Wayland, users will then expect same performance/features like the new ones - and blame Google.