Garet Mang answered...

Well if Jesus Christ decided to have twelve apostles to minister to the people once he was gone, then why would he change his mind and decide not to have them ever again?
The twelve Apostles are like a pedestal, a foundation, where the church which is a beautiful vase is built upon. (Ephesians 2:19-20) When there was twelve and Juda fell away, it was important to replace that lost leg of the pedestal, so they chose Matthias, to replace Juda so the foundation would continue to be strong.
But when all the apostles where killed off, and rejected. It was like pulling a leg off of the pedestal, leg by leg. once you start taking off almost all of them, it becomes very unstable. because all the legs were torn off, the vase fell. And everyone knows when a vase falls, it shatters. There were still bishops around though, and they tried to piece the vase back together, and made it look very similar to what it once was. but there were still cracks in it and it wasn't perfect. And if you place water in that vase, it's going to leak out of the small cracks. Those cracks are small and simple truths, and authority that was lost. Because even the Bishops had to report to the Apostles before they were killed
But because God loves us and is perfect, he had Jesus Christ work through Joseph Smith (A prophet) and created a new Vase exactly like the one he made before (The Church), and a new pedestal (The Twelve Apostles). Because Jesus Christ church was the way he wanted it, and so it is again.