Answer: Because they didnt want the south to have to help clear debts made by new york.
Explanation: dont take my word for it but being a hamilfan this is i beleive how they explained it in the show.
Edit: part of the song cabnit battle from hamilton:
"But Hamilton forgets
His plan would have the government assume state's debts
Now, place your bets as to who that benefits
The very seat of government where Hamilton sits
Oh, if the shoe fits, wear it
If New York's in debt, why should Virginia bear it?
Uh, our debts are paid, I'm afraid
Don't tax the South 'cause we got it made in the shade
In Virginia, we plant seeds in the ground
We create, you just wanna move our money around
This financial plan is an outrageous demand
And it's too many pages for any man to understand"