They (false teachers) are worse off than they were at the beginning (before knowing Christ) if after they have escaped the corruption/ pollutions of the world through knowing Christ, yet they are again entangled in worldly lusts/snares and are overcome/enslaved. They have tasted and seen that the Lord is good yet they choose to reject Him and return to their old sinful way of life. Inexcusable! They may have a form of godliness but they're so dead in their sins. In other words, apostasy (abandoning faith in Christ and deliberately sinning) is worse than unbelief (not having faith in Christ or not having known Christ and sinning in ignorance). To hear the Truth/to see the Light and revert to lies and darkness is worse than never hearing the Truth and seeing the Light at all. These false teachers repudiate the Lord and Savior Jesus Christ in spite of knowing fully Who He is and what He has done. At the same time, they use/misuse His name to lure people for their own gains. They know what is right but they choose to do what is wrong.
"It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the Word of God and the powers of the coming age and who have fallen away, to be brought back to repentance. To their loss they are crucifying the Son of God all over again and subjecting Him to public disgrace." (Hebrews 6:4-6)