Because they do nit know any better nor the truth.
They run around like a chicken with its head cut off yelling, "I'm SAVED!" Assuming they are "IN" as far as salvation goes so they can wave it in front of anyone and appear a little better than others.
They cannot understand when twice Jesus stated, "The one who endures TO THE END is the one who will be saved." (Matthew 10:42; 24:13) Where did Jesus say in the middle of one's life? For no apparent reason, that it be permanent?
"To the end" means either end of one's life or the end of this wicked system of Satan's. Israel as a nation lost its salvation for so constant faithfulness. Ending with the murder of the Messiah, foretold in a hundred divine prophecies. They lost salvation to become just another nation on earth. Judas certainly lost any hopes of salvation betraying Jesus.
Many former faithful ones to God, changed, rebelled, and lost their hopes of salvation. We see God appointed a New Chosen People. Anointed with holy spirit poured out upon them recorded at Acts 2.
Several of those 1st century Christians also failed to.keep salvation by turning against God's will. Likewise today, being faithful now is no guarantee for tomorrow.
Along with that is saying they have been "born again". Trouble with that is one must DIE FIRST. An unfortunate detail overlooked by most. When the Bible speaks of this, it is referring directly to those who are chosen to go to heaven. As the Bible also states, they get their by following Christ wherever he goes. The way Jesus got back to heaven was to die first. Then when he was restored to life, it was back as a spirit creature as he had been for countless eons of time.
So too, any human planning on being chosen for heaven must die first to get their. Then be chosen for a heavenly resurrection. Being BORN AGAIN into the spirit.
That little detail flies right over their heads, they turn when the breeze touches them. While any major change in one's life may be a new or fresh start, it is not being "born again".