Brazil has an insane level of financial fraud and tax evasion. Pix mitigates some of that, but at the cost of privacy - something that Brazilians do not care too much about.
Pix mostly replaces and eats on credit card transactions that were done for the convenience aspect and no the credit aspect. As well as allow a whole new part of the country to accept electronic payments, and although that would increase tax revenue from business it also substantially increase their revenue since there is no x% from card processors and don't require special rented/bought equipment.