Why Do Tax Credits Seem Low?

My daughter and her husband live in Virginia. She is still in college getting a Doctorate degree. She does get a stippen from the college of $13,000 per year. Her husband is a Photographer and makes about $28,000 gross per year. They both just turned 26. They have applied on the Marketplace and only recieved a $2.00 tax credit. The plans we looked at on the Marketplace were unaffordable with such a low credit. Is there something that we are missing? Why can’t young adults who are trying to make it on their own, get more help than this?