A major difference is that an offline bookstore necessitates curation, due to limited physical space. Barring very extreme cases (such as trillions of books requiring petabytes of server space), an online bookstore doesn't require such curation. (An online bookstore could be selective about the titles it highlights in its front pages. But there is no need for making a book completely unavailable through restrictive policies such as these.)
If book stores are curating simply based on physical space then all of them would pick the top 1000 books in order to maximise profits. But they don't. They curate based on the type of books THEY want to sell and that represents them.
