That's because he did not have a wife.
It is difficult to believe that Paul had always been unmarried because of his background and because of who he was. Paul was a member of the Sanhedrin. In Acts 26:10 Paul says, “Which thing I also did in Jerusalem: and many of the saints did I shut up in prison, having received authority from the chief priests; and when they were put to death, I gave my voice against them.” How could he give his voice against them? It was by his vote in the Sanhedrin, which means he was a member of the Sanhedrin. Since Paul was a member of the Sanhedrin, he must have been a married man because that was one of the conditions of membership.
Also, there was an insistence upon Jewish young men to marry. The Mishna said this should be at the age of eighteen. In the Yebhamoth, in the commentary on Genesis 5:2 it states: “A Jew who has no wife is not a man.”
I believe it is an inescapable conclusion that Paul was a married man.
From McGee, J. V. 1997, c1981. Thru the Bible commentary.