As @rbartlet said PubSub is:
For FanOut messages, one source many listeners
Not FanIn Messages, Many Source, one listener.
Twitch doesn’t want to pay for your EBS operations, in the bandwidth and potential abuse and server load on the PubSub from allowing FanIn.
They don’t want someones extension to attempt to bring down PubSub by spamming in a tonne of events when five large broadcasters start a poll on your extension at the same time. And 200,000 people vote at the same time