Its not one to one, but providing digital services is not exactly cheap. Data centers and servers take a lot of costs, both the electricity and salary for a team of ops engineers to keep it running smoothly. The building, conditioning, maintenance, insurance, storage, equipment. To ensure low lag and high download speeds you need several data centers with data caches in different regions of the world. If anything it is actually more risky. If a store closes the stock was already paid for by the the owner to the publisher. Zero risk for the publisher. If Steam goes down, it brings windows of opportunity for sales with it and not a dime is secured. They pay for the uptime and quality of service, not just processing a payment once and a download link with a shitty 72 h expiry time. People expect access to their digital goods 24/7 virtually forever. Steam provides it all with a myriad more of business and client facing services that a physical store would simply be incapable of providing.