If you look at Poe as a value add for existing Quora users, instead of a feature that is going to grow their userbase, it's still a net win for Quora even if GPT agents exist simultaneously.
Poe is not really meant as a value addition for Quora users. Poe was a general AI chat company, like ChatGPT.
Poe's unique selling point was their 'chat agents with customizable instructions/personality' and they were charging people money for this while pretty much building on OpenAI GPT API. They also had an agents store.
During DevDay when Sam announced GPTAgents and store, that was a fundamental threat to Poes existance.