Are Angels Sexless?
The sin of the angels mating with human women & creating the nephilim was so bad that God bound them in chains in tartarus until the judgement. In light of that, other fallen angels would probably not have wanted the same fate, so I don't think they mated with women again after the flood.
Probably, one of Noah's son's wives had tainted genes since the earth was so corrupt that everyone else was destroyed. The sons wouldn't have had many women to choose from & that may be how giants continued after the flood. The genes that were passed on were watered down from the first generation nephilim (half human, half angel) to the rephaim, to the zamzummin, anakim, etc.
Maybe the names describe the amount of nephilim genes they may have had in them. The Bible does not say that angels are sexless & can't have sex. There are male & female angels according to Zechariah 5:9. Jesus says that we will neither give nor be given in marriage but will be like the angels in heaven.
Why would he say that if there were only men angels? Apparently they can't procreate little angels, but they can procreate with humans. We just won't be having sex there because it was apparently intended to be a mortal activity.