Yes, the FCC should be going after Amazon as well. I have more experience with that as an electrical engineer who's just getting into FDA-adjacent work.
But the FCC's position is that if I as an electrical engineer want to sell my neighbor here in the US some custom PCB with an antenna, I need to go through testing that costs many thousands of dollars.
If an EE in Shenzhen wants to sell my neighbor the same PCB over Alibaba, Aliexpress, Banggood, Wish, Temu, Shein, Gearbest, or whatever new discount importer is hot I can't keep up anymore, or Ebay/Amazon/Target/Walmart.com, they're just going to create a listing and import it. The FCC simply cannot keep up.
What I don't understand is how they're getting through Customs and Border Patrol. If I want to ship a spare off-the-shelf PLC digital input card for a machine to one of my customers who has a satellite facility in Mexico, there's a 50% chance it gets held up for a month or more. Meanwhile these big distributors have no issues with air-freight shipments of a GPS jammer or raw testosterone direct to American doorsteps in 3 days.
Edit: it seems obvious to me that the CBP should be partially responsible verifying that stuff going through customs subject to FCC or FDA jurisdiction complies with FCC or FDA regulations, or at least to forward the question to the appropriate agency.