You're describing the way software used to be sold, and that worked fine since really there was very little that needed to be patched over time. It wasn't connected to anything. There was no internet and barely a network. It ran on one specific OS/version that was expected to remain static over years. And app compatibility largely fell on the OS vendor anyway. If your app broke with a new version it was their fault.
Things have changed now.
"paid app at version X, which will get bugfixes indefinitely" - Would you continue maintaining some old version of an app you wrote three years ago that nobody buys anymore? I certainly hope not.
