"but I think the site needs to take responsibility for what it markets

Jim - What makes you think it doen't already...???

First google stat I found - "There are over 5 million marketplace sellers across all Amazon marketplaces.23 Jan 2019"

.. accurate enough for our puposes...

Any customer - you, me, anyone, can freely report a dodgy product or seller,
and expect a response from Amazon within a reasonable time...
5 million sellers takes some significant effort to police..
can't be the easiest job...

Even good sellers complain that Amazon acts too swiftly and harshly against them
if a buyer makes a false complaint...