Why is Master Cheife the only one fighting the war in all 3 Halo games?

[Brendan]

Why is Master Cheife the only one fighting the war in all 3 Halo games?
I know all the other spartans are supose to be dead but in the halo books which take plce between the second first and third game show that spartons did survive reach (cuz they just couldnt keep them dead) in first strike thay find ones that survive and in ghost on onyx they are training spartain threes so why in the worl is the chife still fighting alone??

all the books are said to be real in the story by bungi

 

[Mitchell Hoover]

He is the most experienced i be live that's why you play as him so they send YOU in there and you get the job done ( as usual )

 

[Gerardo Diaz]

At the end Ghosts of Onyx we find out that the Spartans were now trapped in another dimension with no way to get out. So John (A.K.A Master Chief) is the only Spartan left to fight the good fight

 

[Jesus]

first of all the books are before this and the onix one gray team are presume to be dead because they never came back the other spartens are in a shield world so ther not no where neer master chef so there