To counteract complacency, Hebrews warns against neglecting God's invitation of salvation, which He does not guarantee until sanctification has run its course.
Most of the attrition from the truth stems from losing interest. Drifting away is rarely intentional, but the result of choosing to live carnally.
Joash, Amaziah, and Uzziah are kept out of Christ's genealogy. Although they started out well, their hearts were turned away by the end of their lives.
The difference between living forever and eternal life is that longevity does not equate to quality of life. Living forever while enduring pain lacks appeal.