Bob Parsons Alberta wrote:So who buys this kind of jammy over-ripe wine

?
Lots of people buy this kind of "jammy over-ripe wine", Bob. Otherwise, it wouldn't be so popular.
Two things in parallel influenced this:
1. Warmer Growing Conditions
The global climate change conservatives attempt to deny is having a profound effect on ripeness and grape sugars. The average brix for grapes at harvest is quite a bit higher than it used to be; thus the basic natural flavor and texture of the wine being produced is changing. Add in techniques and practices that weren't available or allowed years ago, and you've got a general condition where grapevines can produce significantly more than they used to...and can do it under varying weather conditions. Also add that much of the new wine development has been in areas that are not necessarily suitable for viticulture in the first case, and tend to produce precisely that jammy over-ripe quality.
Thus, our standards are changing, our perceptions are altering, and jammy/ripe is coming closer to being the norm.
I don't drink Layer Cake or SparkyWine(TM), but plenty of people do. And they love it.
2. Prevalent Winemaking Styles
We've all seen trends go awry and overboard. Nature of the biz, actually. We suffered through the worst of the Vanilla Oak Years, where people were doing abominable things to perfectly good wines. We even got to the "200% Oak Regimen", for goodness sake! Same thing with the trend toward what the climate is giving you anyway---advanced phenolic ripeness, more jam, more raisin, more alcohol, heavier texture, richer mouthfeel---and away from the leaner, more acid-driven, heavier tannin classics you and I teethed on.
Just look at Pinot Noir. It used to represent a tiny portion of overall wine volume. It used to be unusual to see PN in places where it is burgeoning now (like, say, Languedoc). Now PN is plated in lots of places where it's not really suited and doesn't really belong in the first place, and is further exacerbated by that trend toward jam/ripeness. As a consequence, there's a lot of PN that doesn't---to me---even resemble Pinot Noir, much less appeal to me. Fortunately, there are enough regions/producers that are still making the ones I do like.
But because I don't like certain styles doesn't mean all that much in the grand scheme of things---because they are selling them to somebody, and those somebody's keep queuing up for more. And as long as folks are making money off of it, it will continue until the vein of ore runs out.