The first scenario happened because of carelessness and ignorance. He saved his seed phrase on a phone without backups. Maybe keeping it in an email would have been safer since he can always have access to it.
The second case was due to a lack of knowledge of how the crypto space works. That person didn't understand that he is now his own bank and should have a seed phrase.
How to keep your seed phrase properly : Write it down in a note , and keep it in safe place (safe from physical attack like water , fire etc) . And put it in a place you can easily remember or access, so that you won’t forget where you put it , because if you lose it you won’t able get it back .
It is advisable to keep your seed phrase safe with a waterproof and fireproof material in case of emergency. Keeping the phrase in different safe locations is also ideal.