Have you ever been in sales?
If the requests are real there would never be 5 thousands, let alone 5 millions (or the vendor would count their lucky stars).
If they are spams that already happens today as well, at scale. AI bot would not change that.
The vendor will never blindly make a sample just based on a single request. There will be back and forth. Maybe require proof that the inquirer is serious.
Sending out RFP to 40 vendors isn't unusual.
The AI bot does change it, random spam emails get ignored already as you say.
A request from an AI agent doesn't, as the parent showed.
Now anyone can source 40 samples from Vietnamese factories and get a response, the sort of request that would only come from a serious buyer before AI agents impersonating humans were a thing.