It seems that Angels were created in finite numbers without the ability to reproduce. The Genesis 6 wives were earth women. For the fallen angels to have children with them would mean possessing an earth man to uses their sexual organs.
What Jesus said here seems to indicate that the angels don't have the capacity to reproduce.
For in the resurrection they neither marry nor are given in marriage, but are like angels in heaven. (Matt. 22:30, ESV)
For when they rise from the dead, they neither marry nor are given in marriage, but are like angels in heaven. (Mark 12:25, ESV)
The sons of this age marry and are given in marriage, 35 but those who are considered worthy to attain to that age and to the resurrection from the dead neither marry nor are given in marriage, 36 for they cannot die anymore, because they are equal to angels and are sons of God, being sons of the resurrection. (Luke 20:34–36, ESV)
Basically the argument is if the angels don't marry, would God give them the ability to bisexually procreate? Why would God create them with a desire they couldn't fulfill? Most certainly God wouldn't expect them to be promiscuous.
This is very hard to argue using biblical reference points. There are the verses quoted in the other answers concerning marriage - but arguably this does not discount reproduction.
Reproduction requires seed. And if you accept the Genesis 6 account as angels procreating with earth women, then that may? provide basis for further arguments.
The other point is that there are no (OK, one possible/dubious/disputable in Isaiah) accounts of ‘female’ angels. So that’s a *possible argument against it.
Then there is Revelation 12 - Michael and his angels vs the Dragon and his angels … how did these ‘angels’ become theirs?
But, bottom line, there is no way to conclusively argue any position - but worse, those taking either position could sit there reasonably comfortably without necessarily needing to argue away contrary points of view - as their foundation is not ‘seen’ as solid.
The old English translation of the Genesis 6 passage lends itself to some unfortunate misunderstandings. The Bible is clear, in Jesus' words no less, that angels do not marry.
For in the resurrection they neither marry, nor are given in marriage, but are as the angels of God in heaven. (Matthew 22:30, KJV)
And the Bible never mentions angels as male, female, husbands, wives, children, or babies. As you suggest in the question, angels do not reproduce.
But in Genesis 6, the KJV translation says:
And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them, That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose. (Genesis 6:1-2, KJV)
This expression "sons of God" is a reference to the Godly men, which were those of the line of Seth. They chose to marry worldly women, and it was this that corrupted their morals and those of their children.
For as many as are led by the Spirit of God, they are the sons of God. (Romans 8:14, KJV)
This question is almost certainly too broad.
Can heavenly beings procreate? Do they have the capacity to inseminate a human female?
“I will put enmity between you and the woman, and between your offspring and her offspring; he shall bruise your head, and you shall bruise his heel.”” Genesis 3:15
Genesis speaks prophetically of a time that the heavenly beings will have offsprings.
What are heavenly beings?
“Yet you have made him a little lower than the heavenly beings and crowned him with glory and honor.” Psalm 8:5
A heavenly being is just a little higher than a human. The distinction is that they are natural and above the natural or supernatural. So they can interact with nature and operate above the laws of nature
“There are heavenly bodies and earthly bodies, but the glory of the heavenly is of one kind, and the glory of the earthly is of another.” 1 Corinthians 15:40
There are only two types of bodies, natural or earthly and heavenly or supernatural bodies.
So the heavenly beings in Genesis 6 did not need to take on bodies of humans, they had bodies and they had seed/DNA. As such all they had to do was abandon their place in the heavens and forcibly impregnate a human woman.
“And the angels who did not stay within their own position of authority, but left their proper dwelling, he has kept in eternal chains under gloomy darkness until the judgment of the great day—” Jude 1:6
If this doesn’t answer your question please let me know or if I need to connect the dots more also let me know.