Why did the Ten Commandments condemn adultery if the men had many wives?

Answer 1

The ten commandments were written to protect the interests of men, not to circumscribe them. At the time, adultery was thought of as sexual relations with the wife of a Jewish man. If a Jewish man had a second wife or had sexual relations with a single woman or a prostitute, this was not seen as adultery. The consequences of this can most clearly be seen in Leviticus 20:10, which prescribes the severest penalties for adultery: "And the man that committeth adultery with another man's wife, even he that committeth adultery with his neighbour's wife, the adulterer and the adulteress shall surely be put to death."

Answer 2

The Ten Commandments condemn adultery because it is considered a violation of the sanctity and commitment of marriage. While men in some historical contexts may have had multiple wives, the commandment is meant to uphold faithfulness and honor within the marital relationship.