I watch a ton of automotive centric channels, hobbyist electronics/PC/home automation/3D printing channels and a few weird niche ones like drain cleaning and dashcams, stuff you would never see (or has never been viable) on TV at least without a bunch of product placement and manufactured drama.
For TV and movies I have my own media server and I just download the stuff I, or friends and family, want to watch but I think the experience, content, and presentation is quite different than what you find on Youtube. They fill different roles for me personally as one is pure entertainment while the other is a mix of educational and entertainment in typically shorter formats.
It may be the phrasing in your original comment. It sounds like you're questioning why anyone would watch videos on YouTube rather than questioning why YouTube is lumped in with traditional streaming service rankings.