Because free-market neo-liberalism has done so much for so many. Take case studies from nations that were force fed (via internal or external forces) neo-liberal reforms - like most of Latin America during the 1980s and compare them to when they broke away from such reforms. Or just look at places like Norway or Sweden and how terrible things are going for their 'big government' economic policies.
The "moderate" public actually support most of the NDP policies.
Also, let me guess, when you say socialism is a failed economic system, you're referring to the Soviet Union, right?