That is precisely my question too. Who or what provides the source-data? Ideally market-data should be freely available to everyone. I understand it is an expe

That is precisely my question too. Who or what provides the source-data? Ideally market-data should be freely available to everyone. I understand it is an expense to provide such data. But it could be mandated by law that anybody operating a stock exchange should provide that data for free, to guarantee efficient markets.