It's primarily a byproduct of age (of the resort and the lonegevity of its owners), density (number of villas), and supply.
DSVI is getting close to 25 years old. There are many owners who have owned at DSVI since the resort was in pre-construction sales. In some cases, the DSVI owners have enjoyed their ownership to and beyond its useful life. In other cases, economics have become a factor. Not only may some owners be motivated to sell their ownership because it's now beyond its useful life to them, but they've gotten their money's worth out of their ownership multiple time over. DSVII is not far beyond DSVI in its lonegevity, and in fact, many of the original DSV owners purchased additional weeks in DSVII in its early days, so there is probably a subset of owners who own in both DSVI and DSVII who are motivated to sell.
Hence, the supply of avaialble weeks for sale is much greater at DSVI and DSVII, than at Canyon Villas (a much younger, less saturated resort). Further, the economics in Palm Desert has changed (for the worse) in my opinion, when MVCI built a mega-resort at Shadow Ridge. That took an economic model that was more favorable to timeshare owners at DVSI and DSVII and ruined it, creating an over-saturated supply.
Fortunate for Canyon Villas owners that Marriott has not yet oversaturated that market, but it seems that the disparity in current pricing between the Palm Desert resorts and Canyon Villas is not that great, which I attribute to the above, and the current economy.
