Why is it that I can download videos from YouTube and Instagram, however it's impossible to download a video from Netflix?

I can download videos from YouTube or Instagram fairly easily by using one of several dozen websites, however I can't do the same for Netflix.

This makes sense, since having downloadable videos would break Netflix's business model, however I was wondering what the technical reason for this was.

In other words, why is it that sites like YouTube or Instagram have videos that can be downloaded, however sites like Netflix have videos that cannot be downloaded?