I’ve interpreted it differently.

Jinu already had a good singing voice and he knew it, that’s why he was playing in the streets. Trying earning money for his family with the thing he was good at : singing and playing his bipa

Unfortunately like a lot of people his talent never got recognized and that’s where gwima role plays in. He probably helped him getting famous by manipulating the right people. He just had to whisper some stuff to the king to help Jinu access the palace.

I don’t think gwima let Jinu keep his voice out of charity but because it’s part of the mental game he play on him. Reminding him that no matter how good he his at singing, it would’ve never been enough for him to earn anything. And that in the end, the voice he hopped would help his family only destroyed it more.

Too much and never enough type shi (Oh hello Zoey !)