Why HaShem Left Sending the Spies to Moshe

Simply G-d does not want us to relay on miracles rather the land should be conquered by natural means. Even more, He additional wants that mankind should strengthen themselves and decide the best way to fulfill G-d’s will without Him providing all the specific methods.

(ספר השיחות תשמ"ח, כרך ב, עמ' 90)