The chief reason the was perception that the NCR did not care about the residents of New Vegas. The NCR simply did not commit enough resources to the lawlessness of the Mojave for the inhabitants of the Mojave Wasteland to consider the NCR a real force for good. Attitudes ranged from apathetic to outright hostile to the NCR, and their perceived corruptness or incompetence. The other reason was the massive influx of so called "NCR squatters" that caused a strain on already scarce resources in Freeside. The NCR tried to support all of the destitute of Freeside but the efforts of a malicious dinglefuck named Pacer caused a rift to open between NCR efforts to help and the goodwill of Freeside. On the Strip, the NCR was hardly respected so long as Mr. House still lived. Of course, all of that changed when the legendary Courier 6 stormed into Mr. House's penthouse and bludgeoned the centuries-year old mogul with a deceased raider's golf culb, but that's a story for another time.