Demand for DL discs aren't too bad actually. From where I am, DL media has fallen in price ... from about $20 a disc to $3.70 a disc for Verbatim stuff. And under $1 a disc for Ritek stuff. The thing is that SL discs have ALSO fallen in price. This keeps DL more expensive than SL.
DL is a lot more difficult to manufacture, the yield rates and QC requirements are probably higher as well as cost of equipment. You can't expect prices of everything to fall just because it's been on the market for a while ...
Demand is there though. Though not as high as SL for sure, it's probably mostly gamers looking to make backups and some movie buffs.
That being said, I do agree, quality is just terrible nowadays :(.