Good point regarding the AGI level, I forgot about the $19,250 threshold. Raising 2019 AGI above $19,250 would cut the credit to 20%, $400, which doesn't make sense to do. Beginning with an AGI of $19,000 you could not add more than $250 of income, and you don't want to cut it too close or risk the credit being cut if your AGI goes even $1 over $19,250 for 2019.
The usefulness of this credit was a bit greater before the standard deduction was doubled by the Tax Cuts and Jobs Act of 2017, but I think it still might not have been possible to utilize the entire $1,000 credit.
