Why does God not show Himself to humans so that they would believe in Him alone, without any partners?

Allah established this world for trial and testing. Therefore, His vision cannot be seen in this world, because if that were to happen, all people would believe, and the wisdom behind their existence in life would be negated. Allah Almighty has clarified that this vision will be for the believers in the Hereafter. In this world, He said to Moses (peace be upon him): "You will not see Me," and the Prophet (peace and blessings be upon him) said: "Know that none of you will see his Lord, the Exalted and Glorified, until he dies." The reason for this is the trial and belief in the unseen. Although Allah has commanded us to believe in the unseen, He has established proofs and evidence for His existence. As for the Hereafter, the disbelievers will not see their Lord, while Allah will honor the believers by granting them His vision, as stated in His saying: "Some faces, that Day, will be radiant, looking at their Lord." And concerning the disbelievers: "Nay! Verily, from their Lord, that Day, they will be veiled."