I'm sure they would love to offer more year round, but they need to draw the line somewhere. My LHBS always have packs of past date random strains that nobody bought. I'm sure part of the fault is with the LHBS, what sells just sells and what doesn't sits.
One lhbs employee was telling me that often times they order less popular strains to make minimums, bundled shopping or hit price tiers. Not sure how true that is, just what one guy told me.