Maybe in the US, in some countries there are no such services at all or the services have much less content than the US versions (while also usually costing more).
Some places have slow/unreliable internet, metered internet, or internet which is slow/metered at peak times. Streaming doesn't work well in such areas as you generally want to watch at peak times.
Some people want to download content at home so they can watch it while they're away from home where they might not have reliable internet access.
Streaming services typically employ some kind of proprietary drm which limits what devices you can use for playback.
The streaming services just don't cut it, with torrents i can download content at night when the connection is fast and have them ready by morning for me to play on any device i want. I can watch them on my way to work on phone/tablet, watch at home on my laptop or tv, i can watch on my rooted android or my linux laptop. I can transcode the video to other formats if i need to.
If a service was available which let me download drm free video files in a standard format i would pay for it, but the current crop of streaming services are unusable for me.