Can anybody explain why polymarket and predictit sustain such different prices? Finding these differences wildly implausible.

Design and software at Apple. Also into AI, philosophy of mind, ethics.

because prediction markets aren’t actually accurate historically speaking

but they should be the same price. it’s a glaring arbitrage

Prediction markets usually aren’t accurate until the moment they are the most accurate. 

There is many other factors than basic arbitrage. Liquidity and user volume and also Polymarket is gated etc. 

Also anecdotally, I don’t think most people have even heard about the other one, I assume the volume and liquidity is much lower = diff swings.