For Siri to be really effective, it has to learn a great deal about the user. If it knows where you work, where you live and what kind of places you like to go, it can really start to tailor itself as it becomes an expert on you individually. This requires a great deal of trust in the institution collecting this data. Siri didn’t have this, but Apple has earned their street cred.
— Jon Pielak, former Siri-iPhone developer