If there is no marriage in heaven, why was there marriage in the Garden of Eden?

Because they are two separate places. Among the angels there is no reproduction; once they are created as individuals, they do not reproduce, so there is something about heaven that will not include reproductive capacity. But the very first thing God told Adam and Eve in Genesis 1:28 was to be fruitful and multiply and fill the earth. That was not an option; it was their first job, and they discovered their purpose right away. They were a completely different kind of creature than the angels, and unlike the angels they were made in the image of God, so they had a special designation and a special job to reproduce, which must be pretty important since it was the first thing given to them. Now, when we get to the new heaven and new earth, there will be no marriage, because by then we will have produced. That is exactly why God wants us to fill the earth to capacity: this life is the one chance to populate the new heaven and new earth. This is it; there will be no more creatures created. That is why birth control is wrong, because whatever we do in God's stead to bring forth life happens here on earth, this one time, so we had better take advantage of it and produce as many citizens for the new heaven and new earth as we can.