How do we account for the testimony of the twelve apostles relating to the Doctrine and Covenants?

In the introduction to the Doctrine and Covenants we find the testimony of the twelve apostles:

The Testimony of the Witnesses to the Book of the Lord’s Commandments, which commandments He gave to His Church through Joseph Smith, Jun., who was appointed by the voice of the Church for this purpose:
We, therefore, feel willing to bear testimony to all the world of mankind, to every creature upon the face of the earth, that the Lord has borne record to our souls, through the Holy Ghost shed forth upon us, that these commandments were given by inspiration of God, and are profitable for all men and are verily true.
We give this testimony unto the world, the Lord being our helper; and it is through the grace of God the Father, and His Son, Jesus Christ, that we are permitted to have this privilege of bearing this testimony unto the world, in the which we rejoice exceedingly, praying the Lord always that the children of men may be profited thereby.
– Church of Jesus Christ of Latter-day Saints – Testimony of the Twelve Apostles to the Truth of the Book of Doctrine and Covenants

Why did none of the twelve apostles ever recant this testimony even when some left the church or were excommunicated?

See:

Church of Jesus Christ of Latter-day Saints – Testimony of the Twelve Apostles to the Truth of the Book of Doctrine and Covenants

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