Why? DRM adds cost and complexity to Netflix's operations. I bet a not insignificant number of customer support issues are related to DRM (e.g. bad drivers).

> They still use it for their own productions and series.

Because that's what their platform is. The vast majority of their content remains licensed, and that licensed content requires DRM. They'd have to run a largely different platform just for their own content to be DRM free and now have customers with inconsistent experiences depending on which content was displayed.