So, what changed? Multiple sources close to Nintendo have now told Eurogamer that, at the end of last year, Japan finalised its plans and had a change of heart: Switch needed the strongest possible launch lineup. In short, Zelda will release in March in North America and Japan. Zelda's launch timing in Europe is still unclear.
One source tells Eurogamer that Japan had always wanted the game to launch in March, and had been uncomfortable waiting until later. Another source says the decision to move ahead with March regardless of Europe was only finalised by committee at the end of last year.
Also key was the desire within Nintendo for the game - first announced for Wii U back in 2013 - to launch in as perfect condition as possible. The lack of Zelda at the Switch's launch could also be mitigated by Nintendo's new 3D Mario, development of which was effectively complete and ready for a March arrival.
More at the source -> Eurogamer