Fnatic didn't come to CS:GO until November. Natus Vincere came to CS:GO even later and while ESC came to CS:GO between the two, the Polish roster refused to make the necessary roster changes needed to become the dominant force they would later become as Vritus.pro. Similarly, Fnatic and Na`Vi needed time to learn CS:GO, time they didn't have when NiP was dunking on them every other week.
The only team that held a candle to NiP was VeryGames, which went on to become Team Titan. VeryGames were good, but somehow, they couldn't ever beat NiP. The problem was partially player performance, but it was also map based. Back then, CS:GO only had five competitive maps, and NiP were amazing at all of them. You couldn't ban them out, while VeryGames chose to focus on four maps and ban Infenro. NiP was never fighting from behind, something they could only really do with such a small map pool.
With VeryGames always beating other teams too, there was barely a chance for anyone else to come and upset NiP. They knew how to beat VeryGames every time, and if VeryGames beat everyone else, they never really had to worry about the X-Factor of another team.