Most passengers I collect, don't talk. They're usually on their phone, or on their laptop, or talking to their companion, if they've got one. They may just want a silent ride, may not like chit chat, etc.
I prefer it that way anyway, better to concentrate on your driving instead.
Also if the conversation turns religious and/or political, you'll have to try and remain neutral, whatever your views are, otherwise it won't be professional.