From what I have gathered, its more about continued breeding and space. Like, if they crossed two strains looking for a certain trait they might let people run some of the seeds before deciding if there's something in there worth looking for and breeding on their own. If not they might try again or something.
Also, from what I've seen they end up with a metric-shit-ton of seeds each grow. Keeping just the grade-a seeds they still have 3/4 of that in seeds that may or may not pop. I'd pay shipping for a handful of factory seconds any day LOL
@HydroRed occasionally asks for someone to drop seeds "NOW" or don't ask, and he'll tell you what he's looking for.
I'm sure the breeders have better answers. Why do they sell some strains while others are designated as "freebies"? Mysteries of the universe. Sometimes it's best to just say thank you and move on LOL