People prefer to use mobile wallet because they want to get easy access to their asset, but it's too risky I agree with you that hardware wallet is the best option, they might use a mobile wallet but they have to keep their private key in the safest place, not in their smartphone storage, if they still keep that sensitive information on their phone once they lose their phone then they will lose all those coins.
It is okay to use mobile wallet, or anything as I also do that in order to trade or spending purpose. But storing your private keys or any of your sensitive data on smartphone, computer or any devices that is possible to get hacked, could be stupid thing.
Anyway, I just read the article and it is pretty helpful for those who need to hide their data, still don't store your private keys on your smartphone!
I understand this risk and I agree with your opinion. smart phones are not a good place to store keys or something.
at least you save the backup file on another device.