Guess what? Samsung doesn't care about long term Android support. They're in it to sell phones. It's better for Samsung if Android's ecosystem continues to drop older phones.
At some point, Apple realized that long term support is a competitive advantage they can leverage. Due to their enormous profits, they can increase their support costs. With their closed ecosystem, Samsung can't come in and pull their shenanigans to undercut Apple.
IMO, Android’s openness is exactly why the Android experience on older phones suck.