Rev. Stoffregen,
While God did not give an explicit command, He DID only create ONE woman for Adam. Aren't you the one who tells us, when you are bashing those mean old conservatives, that actions speak louder than words? And if God had wanted to make 37 women for Adam out his ribs, He could have given Adam 37 more ribs. Right? Or are you trying to box God in?
So, why didn't the ancient Israelites believe that monogamy was God's plan?
Sin had already come into the world.
The first humans in the Garden of Eden, without sin in the world, didn't fair too well.
Jews do not look at Genesis 3 as "the Fall." In their view, humans are constantly exposed to evil impulses, יֶצֶר הָרָע
yetzer hara, they also have impulses for good, יֵצֶר הַטּוֹב
yetzer hatov. The first humans listened to their evil impulses rather than the good ones. Seeking to obey God's commands can help curb the evil impulses and promote the good impulse.
There are no indications that the Israelites saw polygyny or concubinage as evil. Producing children from wives, slaves, and concubines was seen as normal. Abraham did it (Gen 25:6). Half of the 12 tribes came from slave women. Judges 19 tells a story of a Levite (a priest) and his concubine.) David (2 Sam 5:13) and Solomon (1 Kgs 11:3) seem to boast of the great number of women they had as wives and concubines.