Juices that are only available in PG are probably Chinese juices, and often the same Chinese juices by Dekang
Most US juices mixers offer at least one PG/VG blend and many offer every 10% blends
PG - thin, lets through the most flavor, lets through the most of nicotine's TH and irritation, makes thinner visible vapor
VG - thick, dulls/smooths everything PG lets through well, makes thicker more persistent visible vapor
I think most US people like blends of various kinds.
With an atomizer and carts or drip tip you can use any PG/VG you like but if you have a thick mix and are vaping it faster than it wicks and getting burning taste, you may need to thin it with a it with distilled water or edible pure grain alcohol or with a thin juice.
I find stuffing-type cartomizers work well the longest for me with thin light clear juices - 20% or less VG and light/clear for less chance of flavoring sediment that would clog the carto
I think tanks like 20-30% VG but some say 50/50 works OK in tanks
And different vendors make a difference in a particular ratio's thickness - some may leave thick juices thick and some may pre-thin them for good flow.