So long as they keep up with patches that can be fine, but newer kernels also have useful feature improvements. If nothing else, performance tends to improve over time.
In practice upgrading kernel can easily cause performance regressions and cause multiple other issues (reduced battery life) so there's a lot of risk for zero reward for an OEM to do that.
After all, they're on the hook for not breaking users already working devices and don't get anything by risking lawsuits and recalls.
In practice upgrading kernel can easily cause performance regressions and cause multiple other issues (reduced battery life) so there's a lot of risk for zero reward for an OEM to do that.
After all, they're on the hook for not breaking users already working devices and don't get anything by risking lawsuits and recalls.