Why weren't Kise and Midorima able to get in the Zone? According to the anime,


  The Zone, in this state of extreme focus, all unnecessary thoughts disappear and the athlete becomes absorbed in his play. Only those who have practiced and practiced, earn the right to stand before the door and it'll open up.


Since it's shown that Kise and Midorima have practiced more than Aomine and were the members of Generations of Miracles, they were still not able to get in the Zone.

Why?
Kise 


   has already been shown to enter the Zone in the fight against
 Jabberwock. (Read: Kuroko no Basuke: Last Game)


During his state, he can freely copy all moves including moves that he wasn't capable of using, which were moves by Generation of Miracles-tier. 


   He used the Zone in conjunction with his Perfect Copy Ability amping
 up all the skills he currently has.


It is stated in the manga that those who have a passion for the game can enter the Zone. This is shown that even though it appears that Murasakibara had shown a dislike for basketball, that he also, indeed loves to play basketball too. This is one of the pre-requisite to enter the zone.

Knowing Midorima, he can't enter the Zone as he is as of now. He thinks of basketball as nothing more than just a game that he's good at. There's a probability that he can enter the Zone considering he is already is a GoM. All he has to do is to have strong passion/love for Basketball.