Nick just wanted to experiment with more cartoon-based programming as opposed to live action shows, which were more expensive to produce.
Every competitive company exists to make money, regardless of what method they use to do so. In Nick's case, it was getting rid of the live-action shows, slowly, but surely.
Although they kept their studio during this transition, just in case they'd need it, it was eventually closed down because they weren't doing any shows there and they weren't interested in the Universal Studios leasing rate, I'm sure.