What are the reasons for the gradual curtailment of the reforms of the tsar (Alexander the first)

What are the reasons for the gradual curtailment of the reforms of the tsar (Alexander the first) and the refusal to further liberalize domestic life in Russia in 1815-1825?

The reforms of Alexander I were curtailed in 1815-1825 due to the reaction of the conservative nobility, who, after the victory over Napoleon, feared that revolutionary ideas from the defeated France would be transferred to the Russian Empire. Alexander the First was a fairly liberal politician of his time. He had many projects that he and his friends from the Secret Committee wanted to carry out. Among them are the Constitutional Reform, the abolition of serfdom, etc. But after 1815, he focused on military reform and the security of the state from external and internal enemies.