Why is free will necessary?

Answer 1

...behold, all things have been done in the wisdom of him who aknoweth all things. 25 aAdam bfell that men might be; and men care, that they might have djoy.

26 And the aMessiah cometh in the fulness of time, that he may bredeem the children of men from the fall. And because that they are credeemed from the fall they have become dfree forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the elaw at the great and last day, according to the commandments which God hath given.

27 Wherefore, men are afree according to the bflesh; and call things are dgiven them which are expedient unto man. And they are free to echoose fliberty and eternal glife, through the great Mediator of all men, or to choose captivity and death, according to the captivity and power of the devil; for he seeketh that all men might be hmiserable like unto himself.

28 And now, my sons, I would that ye should look to the great aMediator, and hearken unto his great commandments; and be faithful unto his words, and choose eternal life, according to the will of his Holy Spirit;

2 Neph. 2 24-28

Answer 2

Because no one wants to be followed by robots. God wants our love, and wants us to CHOOSE to follow Him.