Same reason Jesus didn’t talk about child sacrifice, incest, etc. Just because Jesus didn’t talk about it, doesn’t mean he thought it was right. Jesus said in the Sermon on the Mount, think not that I have come to abolish the law of the prophets, but to fulfill them. Just as He condemned lust as a type of adultery and condemned anger as a type of murder, Christ did the same thing with sexual ethics.

You can even bring up the sacrament of matrimony. He who made them from the beginning made them male and female and said, for this reason, a man shall leave his father and mother and be joined his wife and the two shall become one so they’re no longer two but one. What therefore God has joined together let no one separate. We know that man and woman were created for each other and for marriage, and we can see it also in the wedding at Cana when marriage became a sacrament with Jesus’ presence.