The Nest team definitely won't agree with your value judgement of these devices, nor do many of the users who paid for them. To this end, even if there are different motivations for different teams and other tactical considerations, it is absolutely necessary for the owning team of a product to have a real motivation for such a significant operation as replacing the entire firmware and runtime in the field. That set of motivations are rooted in the properties of the OS: https://fuchsia.dev/fuchsia-src/concepts