So, you need something else. Despite the fact that manufacturers seem to operate independently of Google, the search giant still has power over them, which stems from licensing Google Play services. Therefore, I would take advantage of this on-site Google and obliged manufacturers to release security updates for all smartphones for three years, and not just recommended. In case of disobedience, the search giant could deprive brands of their services licenses, which would quickly change their attitude towards software support for their devices.