Maybe a better way to ask the question would be: why is the Facebook app so bad?
This is not so much a question specific to the Facebook iOS app, it just uses that as an example. What I want to know is how is it possible that a company like Facebook that has all the resources it needs can make such a bad app. Facebook is famous and "cool" so a lot of devs, designers and architects want to work for them, and it has the money to pay for the best of those. And it's not like it doesn't care about the app. It's not some small internal unimportant project, it's one of the most downloaded apps on the app store. But also one of the most complained about. This brings me to my question, how is it possible that an entity with such resources and desire can end up making such a bad product?
To put it another way, what are the main complexities involved in such a big project that can ultimately lead a collection of perfectly skilled individuals to collectively create something that is not so perfect? Put in a more positive way, what is required (other than skilled people) to make a great product?