On capable devices actual downloading is even supported as an USP by most providers for offline/travel scenarios. Besides that there are even more externalitie

On capable devices actual downloading is even supported as an USP by most providers for offline/travel scenarios. Besides that there are even more externalities that differentiate them: Client and User requirements and targeted devices, therefore mass adoption and market penetration. Downloading requires quite expensive hardware by comparison in usually quite complicated setups for a TV/like experience, it requires the user to do active file management, (which includes deleting files at some point, or buy more expensive local infrastructure) to become a mass market consumer thing, this needs to be externalized. A streaming client is way cheaper to build and market, since doesn't need any relevant amount of non/volatile memory to speak off, that the user experience easier to sell is also quite obvious as witnessed by the golden last decade, it's only now getting tainted by encroaching advertising and platform proliferation etc.