There is no "demand" per se, or if there is, the demand for other things outweigh campaigns. However, people are only too happy to purchase these; after all, what can you do in a "sandbox" sim after you've had your training wheels taken off?

To be fair, it's not ED that is making these but 3rd-party devs or even established community members... what I want to know is what kind of and how much support ED is allocating to these campaigns and why a patch has to be released to "add support" for these campaigns. So even if ED is not making these campaigns, these DLCs still take some of ED's time.