This was only 1,5 years of delay, to be honest, this is not even outrageously long:
Prey was released 11 years after its announcement,
Team fortress 2 was developed for 8 years,
S.T.A.L.K.E.R. was delayed for 6 years,
etc.
etc.
etc.

They simply overestimated the technological challenge, and their manpower.
This happens very often, almost every day, but we don't notice it until it happens with our game.

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