Mostly because from a business perspective there could be a release of a new industry of games and steam wouldn't be able to make any profit off those types of avenues of revenue. In 20 years from now how many blockchain titles will there be and how will distribution platforms be able to take a cut of a portion of the sale if the sale never occurs? Any amount of data spent aiding these types of endeavors is a straight loss of profit with zero chance of recuperating costs