It’s not what you think.
First, it’s not a “x10” issue. That’s silly. Seth wasn’t 10 years old when he had his son Enosh. Enoch wasn’t 6 years old when he had Methuselah. It’s not a math problem.
Second, it’s not a “copy” of the Sumerian, Akkadian, or Babylonian kings, who lived 36,000 years according to their stories. Those kings were god-men, and their kingdoms were glorified. There is no such veneration in Genesis 5.
So what is going on? Why does it seem a little similar to the ancient Mesopotamian stories?
The way to study this is to think less about the characters in the story, and think more about the intended audience of the story.
It is largely assumed that Genesis was written/compiled/edited during a very important time in Jewish history: the Babylonian Exile. It is for this reason that so much of Genesis has such strong anti-Empire undertones. Even the creation account kicks against the Babylonian pantheon, with Tiamat an entire non-participant in the story in the first few verses.
The Tower of Babel, too, is a dig at the expansive Babylonian Empire.
So what of the long-lived kings?
The Genesis 5 account doesn’t show the men as being holy or powerful. It gives almost no attention to their accomplishments, and saves precious few words of elevation for Enoch and Noah. But the big kicker is found in Genesis 6.
In Genesis 6 we learn that the ultimate culmination of this list of long-loved men is… wickedness. Total darkness. It’s so bad that God is grieved at how humanity has imploded. Only a flood will do.
This is a statement about humanity, but more pointedly, it’s a statement about Babylon, which has enslaved the Jewish people. They are a symbol of wickedness.
The flood isn’t God’s anger at humanity. It’s God’s promise of deliverance. He will destroy the Babylonian empire and rescue his people.
So, like many other aspects of Genesis, the story of long-lived men is thumbing the nose at Babylon, teaching us to always thumb our noses at Empire.