They do, but they just pop up as a different seller under a different name with a different business address and the cycle goes on. That's why all the sellers have weird names and make no effort to drive any sort of brand awareness or loyalty.
So mark a vendor as "new vendor", add mandatory ghost shopping to all product skews (postage returns paid by vendor), funds only clear after product arrives + n days for new accouts, etc to build in security that products sold are legitimate. All you need to do is make cost of standing up a scam more expensive than the real thing.
That's something different though somewhat similar.
All that tech, platforms, manpower and literally all the backend data about it (access patterns, descriptions, sales, back accounts, user agents, IPs, everything) and they can't detect something that's blindingly obvious to anyone paying attention?
Even more than that, they require government IDs and other documentation to set up seller accounts, but at the end of the day it's easy to come up with new straw front people for your scam, with clean papers, addresses, and bank accounts.
Noone at Amazon is looking at the id. If they did it would add 'friction'