the mc has never seen anything besides his underground prison, why would he have a dream of going out? this underground prison is all he knows. he should've been a mindless obedient drone at this point.
he also never met his mom, why would he care about her?
it would be something else if the kid was raised normally up until let's say 10 years old. show us that he actually had a life before this prison. then have the mother leave and THEN have his father go crazy. show us that the MC actually lost something, that's why he wants to find it. that would be more believable and actually compelling.
that's why it's such a common trope for characters to get revenge for the death of their loved ones.
if the loved ones were never there to begin with, what's the point of seeking revenge? you've never spent any time with these people, what would compell you to seek retribution on their behalf? I get that the MCs mother is out there but she should've been a total nobody to him. you would not miss something you never had.
the premise that the manhwa has will only work if we actually get to see the kid actually have his happy life get snatched away. if he was isolated since the beginning with no actual frame of reference of what freedom is actually like, then there's nothing for him to long for. he would just be a husk.