Uncle_Sheogorath Sloth is completely right on this one. You aren't forced to read anything, and it entirely up to them what they choose to give out for free. This is not to mention that with the recent changes to the bonus reward, I have been getting more All Work FPs than ever before. A typical example of "don't call the game shit just because you're not good at it".
Anyway, as for manipulation, this is every single marketing campaign used. It is hollywood dictating to you what is "beautiful", it is every advertisement and discount offered to the public. Jesus, there was a bookstore I kept hearing on the radio which was having a "closing down sale" for about 2 years.
It is facebook, google etc using preferences to market specific content towards you. It is the scandal of Amazon recording conversations via Alexa/smart speakers in order to tailor content to you.
I think genre FPs aren't all that bad in comparison. A lot of people complained and they even increased the daily check in bonus rewards.
There is an age old business tactic which is essentially "the consumer doesn't know what they want until you tell them what it is that they want"
Some of these genres have much less traffic so they would obviously like to raise awareness and attract potential customers over. They do so by offering freebies. Whilst it may mean you get one less all works free pass, it may also mean people could find a new favorite novel they hadn't considered trying before.