Fermenting alcohol that tastes good is not easy enough to justify a mass market product. Furthermore, why buy this when you can just buy cheap boxed wine that probably tastes much better than whatever you would get from fermenting reconstituted dry grape concentrate?
I've often made one gallon batches of mead; it's pretty simple, and wine (if you don't get too fancy) is a similar level of difficulty.
IME, one gallon batches about two hours of work from start to a clean kitchen. Five gallon batches take much longer to cool after boiling, so are a much bigger headache.
Yeah, my late grandpa after he retired used to grow some grapes and make wine out of that on his small hobbyist gardening parcel[0]. And at least by the time I grew old enough to be allowed to drink it, he had become good enough at it that it was quite enjoyable and vastly better than cheap boxed or bottled wines in my humble opinion.
His output was like 30 bottles of red and another 30 of white, so in gallons that would be a little more than 21 liters each or 5 gallons each.
He gave away most of it to family and his friends - we had a lot of his bottles on regular barbecues he hosted - and even had my cousin help him design and print funny bottle labels.
[0] A "Schrebergarten" with a small almost-a-shed house.
