Central banks don't print unlimited fiat, they strike a balance between inflation and deflation. Anyone thinking that they can "print unlimited fiat" winds up like Zimbabwe. "Print" too much, and there's inflation. Too little, and there's deflation. But most money isn't printed, it's just balances on bank statements; the central banks control the money supply by regulating banks. With Bitcoin, there's no intelligent control, just rules that produce deflation, meaning it might be attractive as an investment but it doesn't work as currency.