Instead of doing things like securing their supply chains, the reaction of the seed companies is to... just make anyone else selling seeds illegal.

Not quite, the counterfeit seeds here are dramatically worse to the point where buyers will feel scammed and face significant hardship if they mistakenly use them.

Imagine if 90% counterfeit electronics caused house fires, the harm is way beyond the purchase price. At that point customers start caring a great deal, but corruption is difficult to avoid.

It worked so well in the War On Drugs... Don't do the hard work of taking down illegal supply chains; simply put the end consumers into jail for several years!

/s