Convenience
People are almost always willing to surrender some quality for the sake of convenience. A landline is a far more reliable channel with much better sound, versus the cell phone which often drops calls or garbled-up signal. Despite that, I've never had a landline.
“As it turns out, it was true that the iPhone made e-mailing a more cumbersome experience. But it did everything else so much better that it didn’t matter. People were willing to give up some of the ease of e-mail use for everything else iPhones provided. ”