People preserve strains that are good if it is not around it probably wasn't that good. People always look back with rose glasses.
Well its hard to select based on quadrupedal quad dimension Landraces are great genetic baselines of desired traits you can always go back to.
With cannabis I don't think it is that simple. For decades governments were (and mostly still are) trying to wipe out the plant. Most of what has been preserved in North America and Europe have been strains that perform well for commercial growers indoors under artificial lights. That means that growers and breeders intensively bred indicas and indica leaning hybrids and largely ignored tropical sativas. From what I grew in the '80s and early '90s I would say that land race indicas and land race sativas produced high potency individuals at similar frequency but modern strains lean heavily to the indica side. Even "sativas" like Jack Herer and C99 look like 50/50 hybrids when compared to an '80s Mexican or Thai. What this means is that the old, uncrossed sativa lines face a very real risk of disappearing. In many cases they are only being held by one or two growers who grow it for personal use because they like the smoke. If that grower gets popped the line is usually gone for good. With good breeding and grown under tropical sun these lines produce cannabis that is every bit as good or better than modern indoor hybrids but due to the legal situation they represent less than 5% of the genetics that are currently available.People preserve strains that are good if it is not around it probably wasn't that good. People always look back with rose glasses.