The reason why whatsapp can keep it small is because they decide features based on engineering cost first. Does the designer want a feature or UX design that w

The reason why whatsapp can keep it small is because they decide features based on engineering cost first. Does the designer want a feature or UX design that would be a pain in the ass to create with this UX kit? Is there a probably uglier equivalent that would take 1/10th of the engineering time? It gets shot down and we do it the engineer-simpler way. One UX example in the iphone app is the action sheet that pops up when you want to send photos or your location. While in facebook it gets embedded in a fancy keyboard drawer. The action sheet version probably took about 5 hours total for all of it, while facebook messenger's version probably took 500 hours minimum. Another example on the backend is how they are relatively stateless, do not keep chat histories, do not have real multi-device w/ one account capabilities and so on. Each of those features would increase engineering and machine cost, sometimes significantly.