All the seeds that just any jerk can buy are all these heirloom seeds.
Given that the vast majority of seeds I see in catalogs are F1 hybrids, it's unlikely that your statement is even remotely true. Most of what is sold to home gardeners is the same varieties being sold to commercial growers. Most home garden catalog vendors are in turn purchasing their seed from the big boys that supply farmers - Northup King, Stokes, and so on.
There are a few - Territorial Seed and Johnny's Selected Seeds come to mind - that to some degree also actively work on developing their own seed stocks; but even with them, most of the seed is being purchased from a handful of huge companies.
The only places I see heirlooms dominating a company's listings is in catalogs from companies specializing in open-pollinated vegetables - Seeds of Change, Abundant Life, etc.