The answer is because it is easier to feel smug about one's performance in external areas than it is in matters of the heart. For another thing, the verses in question do not concern heavenly entrance. Rather, they concern heavenly inheritance. That is a big difference. Space doesn't allow more than a statement of conclusions here.
Inheritance refers to what parents leave their children.
A true child may be disinherited. Yet she remained a child in the family, attended family get-togethers, etc. Believers whose lives are characterized by things like covetousness, jealousy, murder, and the like will not inherit in the sense that they will not rule with Christ. Many things are conditioned upon ongoing obedience for the Christian. I marvel at those who charge us in the Free Grace camp of teaching that obedience is optional in the Christian life.