Because the Minitel was completely vertivally integrated. The terminals, software it ran (as the "OS"), Network and billing were all handled by one entity. And

Because the Minitel was completely vertivally integrated. The terminals, software it ran (as the "OS"), Network and billing were all handled by one entity. And only this entity could approve software for distribution. It was a completely centralized walled garden. Office, Netflix, Youtube Premium, Spotify, Blackblaze can all run anywhere, and on platforms such as Windows are free to do their own distribution.