1. It was in development for an eternity and underwent at least two major redesigns. I'm guessing it had a crazy high development cost and, while the overall final product was good, the price tag turned Nick off to making any long term commitment.
2. By the time it was ready, Nick was undergoing an office coup and the CEO and many top ranking execs were getting ousted. Glitch Techs was a creation of the old regime, and it was sitting unreleased with a high price tag, the new regime had no stomach for untested shows beyond the umbrella of the Loud+Sponge+LiveAction trio that had been working great for the channel. Thus it was pawned off to Netflix.
3. Wasn't really marketed well, it just appeared on Netflix, and its second season's release was overshadowed by Korra being released at the same time.
4. The creator was kind of an ass. I know his heart was trying to be in the right place (he didn't want kids searching the #glitchtechs tag to see Miko getting railed in 9 out of 10 posts) but he had no grasp of how the internet worked and his nastiness could be read through his tweets makes one wonder if his work place attitude may have had an effect on this show's treatment.