So, what is the basis of being sent to the LOF then?
Real simple. Both the Bema and GWT judgments are judgments based on works. Both of them.
Bema is for believers only: 2 Cor 5:10 - For we (believers) must all appear before the judgment seat of Christ, so that each of us may receive what is due us for the things done while in the body, whether good or bad.
This judgment will determine whether the believer earned reward or not.
GWT judgment is for unbelievers only: Rev 20:11-15
11 Then I saw a great white throne and him who was seated on it. The earth and the heavens fled from his presence, and there was no place for them.
12 And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life.
The dead were judged according to what they had done as recorded in the books.
13 The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what they had done.
14 Then death and Hades were thrown into the lake of fire. The lake of fire is the second death.
15 Anyone whose name was not found written in the book of life was thrown into the lake of fire.
Works won't determine whether anyone will be thrown into the LOF. Rather, the GWT judgment will determine how "tolerable" or "bearable" it will be for the unbeliever.
We know this from what Jesus said:
Matt 10:15 -
15 Truly I tell you, it will be
more bearable for Sodom and Gomorrah on the day of judgment than for that town.