See my previous answer RE: Zecharia Sitchin for an interesting and literal interpretation of this and related texts.
In a nutshell. God required a worker in his 'garden', mankind was that worker, created in His image; a clever and able worker. However, mankind could not procreate. Satan provided mankind with the requisite capability ('knowledge' ) to procreate- see the Garden of Eden scriptures. God was far from happy about this (Genesis 3).
Onr of the outcome of mankinds newfound ability to procreate was of course the 'daughters of men'; they were found to be quite attractive (and available) to the other gods even though they were forbidden from acting upon their desires. They couldn't resist though.......(Genesis 6)
Look at this from the Daughters of Men perspective, they could entice and attract the gods, with their charms: quite a catch really. After which, us ordinary fellows were of little value to them and pail into insignificance. (I don't think things have changed too much nowadays either!)
And God was far from happy about all of this as well, blaming both Satan and (sadly) mankind for the resulting outcome, as 'we' multipied rapidly across the planet. (Genesis 6.) That is why He was indifferent to the impending Flood which would wipe out the planet...