a commercial $3/bottle of merlot is bulk wine plain and simple, the same wine that many countries overproduce and end up turning into industrial alcohol. where volume is the vineyard's key motivator - very little attention is paid to cluster quality, ripeness, sugar levels, etc, it is about maximizing yield. stressed vines and low yields make the best grapes because everything the vine has left is going into those few grapes - not into foliage and canopy.
personally i don't understand the point of $3 commercial wine. at that pricepoint anyone can make a wine at home that will surpass it in quality.
for myself, i draw the line at about $9 for commercial wine...and that's mostly spain, portugal, argentina, south africa... where bargains can still be found offering good quality at reasonable prices.
while acidity probably plays some role - i think it is contributory. the key fault is that the juice was not good to start with, if you don't start with the best juice, you cannot make the best wine.