These exit companies are scams, all of them. During the years I was an HOA board member at a sold out resort, we would always negotiate with our owners on a deed back, because it was quicker and cheaper for the HOA than going through a foreclosure. I have heard that some developers can be jerks to deal with, of course, but most will see reason.
One of the worst scams I have seen was one of these exit companies taking thousands of dollars from a widow to "exit" three summer weeks on the Outer Banks, at least one of which at Barrier Island Station Duck. Those weeks could easily have been sold on the OBX resale market for at least a couple of thousand each, but his "exit company" scammed the woman to pay them thousands and then turned around and sold the weeks on eBay.
The market value of a timeshare depends on location, season, maintenance fee, and market demand. Some do have only marginal value, but some have a decent value and are easy to sell. The exit company cons you out of thousands, regardless of which category your week falls into.