The smartwatch hardware are designed with a particular OS in mind. The older smartwatches that originated with Android Wear or Tizen have limited upgrade options within themselves. For example, if you have a Tizen OS, you may be able to upgrade to a newer Tizen OS. However, most watches that are not using Wear OS 3, cannot be upgraded to the latest OS. Not even Android West OS watch can be upgraded.
It is hoped that as Wear OS 3 matures, those watches will be more easily upgraded to new OS versions.
