Perhaps that is just the style most make for muscadine wine.
Though there are some forms of sugar that yeast don’t consume, wine grapes and muscadine grapes have a similar range of sugars from what I read.
Many recipes for wine add raw sugar in some form into the must to increase the end result alcohol percentage, so I’m thinking it’s not having too much sugar in the muscadine itself that makes the wine sweet.
There are some forms of sugar present in wine grapes, and I’m sure also in muscadines that are not consumed by the wine yeast, so it would be true to say no wine is truly 100% dry, but effectively so.
I enjoy a slightly wine like a Gewurztraminer as a drinking wine and don’t mine a sip or three of a dessert wine or port, but no more than 1 glass.
I am in Texas 8A so my 8A may be different than yours. California can be hot inland or milder near the coasts so hard to say if my experience is helpful. We have 100 degree summers here. Paulk I have tried twice to get established and it died both times. Big Red I have no experience with. The ones that have been very good here and exceptionally productive are Summit, Triumph, and Hall. Lots of grapes and these are all bronze varieties. The others I grow are much less productive or have very small grapes. The less productive ones are Southland, Cowart, Late Fry, Sugargate and Black Loomis. The ones that are productive but have small grapes are Dixie, Alachua and Noble. Noble produces massive amounts more than any other but are the smallest of them all. So maybe for juicing and wine it might be good, it is a black variety. Dixie and Alachua produce ok, not great, but are small. Southland and Cowart are small too but produce very few grapes. Note this in the Texas 8A environment and different varieties do better or worse in different locations. But Summit, Triumph and Hall have been my super stars. I have not been able to get Paulk, Black Beauty, Early Fry, Late Fry and Sweet Mix established here. I have been trying to find a large productive black variety that will work here but no luck. Sugargate is large but not productive. If you are coastal 8A in CA your experience will be different, if central CA 8A might be similar but we are a bit hotter than Central CA 8A.