Keep the prices low? Their oil is almost double what synthetic oil prices are at Walmart.
You can switch back an forth between any oil as long as it meets the API (or higher) and viscosity recommended for the vehicle.
Amsoil may be the best oil ever made. But so what? Any good oil will keep good designed and built vehicle well past 300k miles. From my personal experience - I’d say far less then 1% of us keep vehicles that long. Not even close. So what is Amsoil giving you?