For mercenaries, eight out of ten are gamblers, and at least nine out of ten love the flesh-to-flesh freedom of combat. Combining these two elements, few could resist the temptation.
The Aziziya Barracks now were like a volcano's crater, where anyone who jumped in could only wait for the eruption. Gaddafi's rule was tottering; it was only a matter of time before the opposition took over completely. As one of the symbols of Gaddafi's rule, the Aziziya Barracks were inevitably a prime target for the opposition.
If no accidents occurred, the mercenaries staying at the Aziziya Barracks were essentially waiting for death. Even though they were paid a lot every day, the pessimistic outlook made it seem impossible for them to spend their money. Thus, it made sense to bet all they had in a desperate gambit for exhilaration.