This is a secondary cause, that while true came much later. The earliest cause is 1 Corinthians 7 where St. Paul indicates that the unmarried state is superior. That is why many of the Apostles, who started out married, embraced unmarried life after the passing of their wives. Matthew 19:12 is also relevant, as I do not want to imply this idea rests solely on the Apostle St. Paul.