For what it is worth, in case you want to make your own grape jam.
The recipe calls for basically four things: grapes, sugar, lemon, butter. And as I have gotten a lot of recipes off of SeriousEats.com, I figure this might be worth a look.
Check it out here.
TL;DR: likely because demand was too low to sustain commercial distribution
Barring any relationship to a specific historical incident, it's very difficult to find out why a specific food is no longer commercially produced. In the absence of specific reasons, we can see a number of contributing factors as to why grape preserves would have gone off the ...