Also consider the Nigerian government current receives aid money, plus whatever amount they're able to tax from this fraudulent money (which is probably pretty

Also consider the Nigerian government current receives aid money, plus whatever amount they're able to tax from this fraudulent money (which is probably pretty low as you mentioned, fraudsters are unlikely to be on the up-n-up with their taxes, especially when the income came from illicit activities). So chopping nearly $1 Billion in aid is going to hurt badly, even if the fraud continues as normal.