Yeah, but you don’t need to ship an entire OS with your apps. You only need to ship your app code. The user’s software distribution should handle the rest.
Discussion
I can understand your argument. I think you could see it as a tradeoff between disk space and development time.
If you want your app to run in different configurations, you'd have to test and develop for all of those. Currently, disk space is cheap and development time isn't, so it's a reasonable compromise from an economic view. 🤷