What is the wisdom behind God's ordination of 50 prayers, when He, glory be to Him, knew that the Ummah would not be able to perform them?

The prayers were initially fifty, then Allah reduced them to five, as a grace and mercy from Him upon the Ummah. Among the reasons for this reduction was to demonstrate the honor and high status of Prophet Muhammad, peace be upon him, with his Lord, by accepting his intercession and his plea for the reduction. This also shows the importance of persistent supplication to Allah, and the virtue and compassion of Prophet Moses towards the Ummah of Muhammad. They are five prayers in number, and fifty prayers in reward.