If your key is stored on a device that has an internet connection, you are trusting a third party not to confiscate your keys. You’re also playing a lottery with whether or not that device is exposed to attackers. Never store keys to bitcoin you absolutely don’t want to lose on a hot device, period. Why is Balaji not just saying that?
Discussion
(The answer is that alluding to technically-possible drama of an Apple-Google-USG conspiracy to attack bitcoin holders will get way more engagement.)