Why exactly is Thrace so CHP anyway? It's fairly rural iirc.
Main divisions in Turkish electoral politics aren't urban/rural (that's a comforting myth put out by urban middle class opponents of the regime and recycled in the international press without checking) but cultural. Areas that saw significant population exchanges/ethnic cleansing/resettlement during the transition from Empire to Republic are usually very loyal to the CHP or at least have large numbers of people who are; areas with more settled populations now vote solidly AKP. And people from the latter take their voting habits to them when/if they move to the cities: this is why the AKP is dominant in the Istanbul slums.