David Guzik comments on why there are 12 tribes, although defined with variation:
"12 is a number often associated with government or administration in God’s eyes. There are 12 tribes, 12 apostles, 12 princes of Ishmael, 12 pillars on Moses’ altar, 12 stones on the high priest’s breastplate, 12 cakes of showbread, 12 silver platters, silver bowls, and gold pans for the service of the tabernacle, 12 spies to search out the land, 12 memorial stones, 12 governors under Solomon, 12 stones in Elijah’s altar, 12 in each group of musicians and singers for Israel’s worship, 12 hours in a day, 12 months in a year, 12 Ephesian men filled with the Holy Spirit, 12,000 from 12 tribes sealed and preserved through the tribulation, heaven has 12 gates of 12 pearls, and 12 angels at the gates, the New Jerusalem has 12 foundations, each with the names of the 12 apostles of the Lamb, it’s length, breadth, and height are all 12,000 furlongs, and the tree of life in heaven has 12 fruits. The number 12 is special to God!"