Earlier quoted context omitted.
I only met techies who cared about continuing to use a phone if they could only boot from their SD card. Regular people don't know about the option. So consider that this niche feature you find useful is of almost no consequence to anybody. Additionally, iPhones and Samsung devices have really durable internal storage. Almost always the battery craps out first.
It's not about trying to boot off the micro-SD card, it is being able to just pop out the card, and get all the data that was stored on it.
The ability to do offline salvaging does not seem like such a big selling point to me.