The airport is closed because there was no strong business model for opening in the first place. Consistent profits were never returned and any ROI just wasn't there. The brutal truth is that the totality of the whole DSA passenger operation has been effortlessly absorbed by nearby airports without as much as a ripple. DSA had no USP, no differentiator. There needed to be a critical mass to stand any chance of being consistently profitable, they never got it. See also Southend and possibly Teesside, both of which are IMHO, similar.
Heartbreaking from one standpoint, but unless you openly operate as public service, that's how it works out.