Is signing up for an Amazon service any different to opting into something like DoorDash or Seamless? Amazon is big/established and probably has the data necessary to understand exactly when they can screw you. They also have a large enough customer base that they will take steps to automate a large percentage of day-to-day operational decision making which will occasionally go wrong such as detecting and shutting down fraudulent seller accounts as exemplified by your reddit link.

A funded startup on the other hand could go under at moment when their next round of funding doesn't come in. It's also a sure bet that any success you're seeing from them early on will diminish over as they attempt to actually make a profit.