That’s a bad reason to make (or keep) something illegal. Having legal weed does nothing to stop enthusiasts breeding their own strains or propagating ‘heirloom’ varieties - because they were already doing that illegally since forever before it was legalized.

Put another way, swap weed for alcohol. Should alcohol be banned because Anheuser-Beusch ans InBev exist and lobbies the government for favourable legislation? No… Fighting against the crap legislation is a better idea, and who would be better positioned to do that than an industry growers union or an independent growers union or similar.

Making something legal or illegal doesn’t magically make it immune to capitalism, it just goes back to a black market where you have no protections as a buyer nor as a seller.