If Mormonism is true and the apostasy started after Jesus' ascension why did God take so long to do something about it when Smith showed up in 1820?

Close to 2,000 years elapsed after the ascension of Jesus Christ and the death of His Apostles until Joseph Smith had his first vision in 1820. In that vision Smith was told by two personages (presumably God the Father and the Son) that he must join none of the current churches because they were all corrupt. Apparently, men corrupted the principles of the gospel and made unauthorized changes in Church organization and priesthood ordinances. This is explained in detail here: https://www.churchofjesuschrist.org/study/manual/gospel-topics/apostasy?lang=eng It should be noted that in the Bible God anticipated this would happen and there are strong warnings for those who apostatized. 1 John 2:19, "They went out from us but they were not really of us; for if they had been of us, they would have remained with us; but they went out, in order that it might be shown that they all are not of us." There is also the Parable of the Wheat and the Tares that Jesus spoke of at Matthew 13:24-30. And what the Apostle Paul said at 2 Corinthians 13:5, "Test yourselves to see if you are in the faith, examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you--unless you fail the test?" Eventually apostates will be made known by their fruit, Matthew 7:16-20. So again, why did it take so long for God to do something about apostasy when He "supposedly" appeared to Joseph Smith in 1820? In view of this fact even before the resurrection of Jesus, He and His Apostles warned us that this would happen and how to recognize apostasy.