Why do Muslim scholars not agree on unifying fatwas, especially since the disparity in fatwas among the schools of thought causes confusion among ordinary people, and is it possible to hold a conference to unify them?

The disagreement among the Mujtahid Imams is a mercy from Allah, because Allah Almighty made the evidences probabilistic (dhanniyyah) to provide ease for those obligated (mukallafīn). There is no blame upon the people of knowledge for their disagreements, and it is not permissible for a Mujtahid to abandon his own ijtihad and imitate another.