Why? An HDCP capable display can show content without HDCP or with HDCP so in what way is one that only supports non HDCP inputs better?

The only benefit is if only a small minority of people have HDCP displays then it makes no commercial sense to mandate HDCP for content. And in my view it is too late for that.

Edit: Note that it wouldn't be a show stopper for me with a product like this but I would regard HDCP support in a monitor to be a benefit.

Edit2: Added missing word to second sentence.

Just wanted to add another item which is that HDCP is completely broken now anyway. The remaining security is mostly the fact that it is bloody hard to handle the massive datarate of the the uncompressed video without custom hardware.

And why bother; almost everything is available in the compressed form (e.g. Blu-ray) more easily accessible if you are trying to access the content.