Why did justinian i fail to regain all of the formerly provinces of the old roman empire

As we all known that Justinian's attempts to restore peace and stability in the territory of the Byzantine Empire turned into cruelty and bloodshed.

Therefore, the restoration of the Roman Empire required huge sums of money, and the people could not bear the constant taxes on military expenditures. Captured territories resisted politics of Byzantium, there constantly erupted uprisings. The historical development of the country cannot be stopped or rotated at will. It is impossible to return the old orders, especially without the support of the local population.

although the crusades failed to capture jerusalem, they had several major impacts on western europe. they increased the authority of the king: sometimes nobles died in battle without leaving an heir in which case the king got their land. kings passed taxes to pay for the crusades.