Catholic priests don’t marry, everyone knows that. Some think it has always been this way, yet it was not until 1139 at the Second Lateran Council that this position was officially codified. Before 1139, most priests did not marry, but some did, and they had a roughly similar policy to Eastern Orthodox. That is, if you are married before you are ordained, you can be married. If you try to marry after you are ordained, you cannot. There are some married Eastern Rite Catholic priests who are still in communion with Rome, as well as former Lutheran or Episcopal priests who become Catholic, but it is important to remember that this was not an ancient policy when it was challenged during the Reformation. When Martin Luther married Katerina, he was not upending 1500 years of teaching but only a little over 300.
Theologically, the marriedness or singleness of ministers comes down to how we interpret 1 Corinthians 7. In 2 Timothy and other passages, a bishop is said to be husband of one wife, so there is some precedent. Yet in 1 Corinthians, Paul says that it is best to not be married so as to more dedicated to God, but if you must, marriage is good.
For Rome, priests were to be held up to the highest standard, that is also why ordination is a special sacrament on its own.
For Protestants, it is the individual and not the institution that decides on marriage. Ordination is not a sacrament akin to Communion or Baptism. It is a blessing and a setting apart for a specific mission of Word, Table, Order, and Service. Immediately after the Reformation, every Anglican priest did not marry. Most early Methodist circuit riders were not married.
Today, though, the tides have turned. There is an assumption that the preacher be married, or if not, they would love to be with someone's granddaughter or grandson. I have a number of colleagues who are struggling in ministry because of these assumptions. I know a lot of churches who think a pastor's spouse is automatically another pastor who will do whatever anyone wants.
Marriage does not bring salvation. Our spouse is not our savior. Our future is not unidirectional. We are not less human single or widowed. We find our hope, our future, our life in the Lord of Heaven and Earth, Jesus Christ. Marriage is not restricted from Clergy, nor is it required. Just like marriage is not required of our children or grandchildren. They don't need to marry to be happy. They can find joy in the Lord.
I lift up my eyes to the mountains—where does my help come from? My help comes from the Lord, the Maker of heaven and earth. - Psalm 121:1-2
Article XXI — Of the Marriage of Ministers
The ministers of Christ are not commanded by God's law either to vow the estate of single life, or to abstain from marriage; therefore it is lawful for them, as for all other Christians, to marry at their own discretion, as they shall judge the same to serve best to godliness.