The economics are different, Safari is a niche product and will always be more expensive than something aimed at the general consumer.
I want to read O'Reilly books as PDFs. Properly typeset PDFs. And I don't want to buy from anyone other than O'Reilly. And I tried Safari, but it's not the same as reading their books as PDFs.
I bought your Spring books, and a few others. Next time I want to buy a book, I'll go straight to Manning and not O'Reilly.