Just about every consumable product we buy, for the garden, or any other part of life, is bought by weight or volume - But not growbags.
Why should they be any different? It is impossible to compare value when we don't have this detail, and I am quite certain that they have been getting smaller, from some outfits, year on year.
What devious marketing loophole are the manufacturers able to exploit in order to keep this information from us?
JeremyB