That's because DVD-makers like Germany's Bertelsmann or Canada's Cinram have to buy whole new machines for producing Blu-Ray discs, but they only have to upgrade their current disc-making machines to make HD DVDs.
However, because the new media specifications are extensions of current Blu-ray Disc technology, future BDXL and IH-BD devices can be designed to support existing 25GB and 50GB Blu-ray Discs.