In Chapter 5 of Genesis we learned that in a time when humans lived 800-1000 years, if Adam was the first generation, then Noah was in the tenth generation. These facts are a bit important, so advise the reader to keep them in mind as we move on to Chapter 6.
Genesis 6:1-6:
1 And it came to pass, when men began to multiply on the face of the earth, and daughters were born unto them,
2 That the sons of God saw the daughters of men that they were fair; and they took them wives of all which they chose.
3 And the LORD said, My spirit shall not always strive with man, for that he also is flesh: yet his days shall be an hundred and twenty years.
4 There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.
5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
So The Jesus realizes that man is able to live way too long and since men are allowed to take any and all woman they choose, the land is becoming full of humans.
Worse yet, The Jesus made man in his own image, which goes a long way to explain the psyche of his creation. The Jesus wanted to create something wonderful, but he ended up creating man instead.