As an early Nest employee who worked on the first-gen thermostat I can tell you definitively that you're way off base here. That doesn't mean that Google shouldn't have done more to keep these units alive (and indeed that's one of the reasons I left Google). But these devices were designed in 2010-11. Even keeping the Linux kernel up to date with the latest version is a major undertaking. Adding major functionality like Matter compatibility, or even a simple (but secure!) local API, would take a seasoned engineering team a considerable amount of time.
That said, investing in devices that are local first is certainly good advice, provided the APIs are open and well supported.
That said, investing in devices that are local first is certainly good advice, provided the APIs are open and well supported.