In a post he made on Twitter, Kojima wrote, “MGSV Ground Zeroes includes the main mission alongside 5 Side Ops. All missions include elements such as “Trial Records,” where players can compete against each other online. This is not a linear game like the past. GZ offers freedom of approach & play style, which we hope players will enjoy over & over without boring. I believe people will be satisfied with the “Play Time” of GZ and will not stress the “Clear Time,” which is a standard for linear games.”
Basically what we can take away from this is that Ground Zeroes is meant to be a game that can be replayed over and over again, which might explain why the “clear time” is short. Either way we guess we will have to wait for the game to be released to see if Kojima’s statements are true and that will happen on the 18th of March 2014.