Here is a different angle to look at it. It isn’t an accepted mainstream view but it does have explanatory power.
Here is a little background context to the whole premise.
Genesis 6 the elohim have intercourse with human women and the enmity between the seeds spoken about in Genesis 3 between the seed of the “serpent” and the seed of the woman begins.
The seed of the elohim contaminate the human gene pool, except Noah and his wife and three sons. Then Elohim decides that the earth is so corrupted that He wipes out everything. Unfortunately the seed/genetics lingers because the wives the sons of Noah took were contaminated.
We see Noah cursing his grandson Canaan rather than his father Ham possibly because he had traits of the elohim seed that were visible and this caused his father Ham to try and have a child through his mother who he knew did not have corrupted seed, knowing he would have very little chance convincing his brothers to share their wives.
The lineage of Ham is littered with the seed of the elohim. One of the descendants is the Amorites. We have many examples including the giant king Og.
When it says that the iniquity of the Amorites has not reached its fullness, one way of looking at it is that there was still a chance to eliminate the gene pool of the seed of the elohim. However it seems that they preferred to not only maintain the seed but exploit the seed probably because it has some phenotypical manifestation like giants, six digits, oblong heads, abnormal fur growth.
There are some curious verses to consider.
“"Yet it was I who destroyed the Amorite before them, whose height was like the height of the cedars and who was as strong as the oaks; I destroyed his fruit above and his roots beneath.”
Amos 2:9 ESV
Cedar trees are known to grow anywhere from 20’-60’+
Also consider this verse that speaks of Ephron whose name means fawn like or part human part goat.
”And he said to them, "If you are willing that I should bury my dead out of my sight, hear me and entreat for me Ephron the son of Zohar,”
Genesis 23:8 ESV
He was a Hittite who is also a descendant of Canaan like the Amorites.
“Benaiah the son of Jehoiada, the son of a valiant man of Kabzeel, who had done many acts; he slew two lionlike men of Moab: also he went down and slew a lion in a pit in a snowy day.”
1 Chronicles 11:22 KJV
That is part lion and part human and in the same verse it also speaks of a human Benaiah and of a lion as distinctions from lionlike men.
Moabites are descendants of Lot but Elohim forbid Israel to intermarry and therefore mix seed with the canaanites, Moab obviously did intermarry (at least in this context).
So when it says that their iniquity has not reached its fullness, like in the time of Noah when the earth was destroyed through a world wide flood, in similar way the Canaanite nations like the Amorites still had a chance of correcting course, genetically speaking.
It is also presumed that the seed of the elohim brings about a complete predisposition to violence and sin
“The earth also was corrupt before God, and the earth was filled with violence. And God looked upon the earth, and, behold, it was corrupt; for all flesh had corrupted his way upon the earth.”
Genesis 6:11-12 KJV
That is why Elohim also ordered the complete annihilation of those Canaanites because their seed or genetics were irredeemable. They past the point of no return. It’s posdible they had created a reversal where the human gene was completely removed and now only elohim genes were being transmitted. Whereas the elohim were not given to marry and have descendants even though they had seed.
Like I said it has a lot of explanatory power. It also have Biblical backing but it’s controversial because most ascribe to the augustinian sons of G-d being the descendants of Seth and not elohim or ‘angelic talking serpentinelike beings’ that took on human form.