They can. You know they can, others (ie: the pirate versions you mention) do. Larger files consume more bandwidth and storage on the CDN, which makes it more expensive. And while there are indeed some issues with lower quality (especially in dark scenes, I'm reminded of the muddy mess in the final episodes of Game of Thrones), most folks are "fine" with the quality we get today. Fine enough, anyway, that they keep paying for the status quo.
That's not to say that they're not interested in providing more quality. There's heavy investment in per-video, and sometimes per-video-section encoding and next generation codecs like AV1. The goal for them though is to get more quality with the same or less storage and bandwidth budget.
That's not to say that they're not interested in providing more quality. There's heavy investment in per-video, and sometimes per-video-section encoding and next generation codecs like AV1. The goal for them though is to get more quality with the same or less storage and bandwidth budget.