Except that most people don't think of their lives as "problems", not "big problems" (more like little annoyances), and definitely not "problems that can be fixed by software".
Source - had same idea, surveyed 50 random people on the street.
But, by interviewing them, they might be able to find those annoyances and those problem areas. A skilled interviewer could probably find potentially solvable problems, that others may not have considered.
Fill in dummy details with a mailinator account and 4242424242424242 card number, to see if I’m interested in paying for this, without disclosing a genuine card number because seriously, why would I trust you…
That seems to be a pretty great way to uncover lucrative startup ideas in markets that you never could have imagined.