In the early days of the PacktLib product Packt refrained from allowing their content being placed on SafariBooks however their product made little and SafariBooks was generating very large revenues for partners so they went all in and that's why they are now a large part of SafariBooks.

You can even buy Packt ebooks from the O'Reilly site now which shows the extent that Packt benefits from selling its content through O'Reilly (and indicates how much it lost out on by not being the other half of SafariBooks)