Having taught against deathbed repentance (a change of heart) they could not avail themselves of it.
Fear of death, at the level described, is a scriptural confirmation of their captive state, in which they misled others too (Matt 23:15):
(Hebrews 2:15) . . .[that] he might emancipate all those who for fear of death were subject to slavery all through their lives.
(Matthew 23:15) . . .“Woe to YOU, scribes and Pharisees, hypocrites! because YOU traverse sea and dry land to make one proselyte, and when he becomes one YOU make him a subject for Ge·hen′na twice as much so as yourselves.