There are many reasons for individuals to enter the gladiatorial realm of Abaddon. Some are tempted by the prospect of wealth and fame, others are forced as punishment for their worldly sins, and some have even forgotten why they entered in the first place.
Lucifer -high overlord of the Abaddon Arena- is a powerful and devious demon who knows exactly how to manipulate fighters into staying in Abaddon, forever. Poor souls who thought they could out-play the devil himself, but alas, it’s impossible. If you dance with the devil, then you haven't got a clue, for you think you'll change the devil, but the devil changes you.
Lucifer realized the potential of an infernal arena upon observing the aggressive tendencies tortured souls acquire after being tormented for a few millennia. Such vicious hostility could surely be used to inflict further punishment, and so he pitted them against one another and had them fight. Soon enough powerful mortals were vying for the chance of fighting one of these monstrous souls and earning a favor from the devil, unwittingly tainting their souls in the process. Gambling rings quickly formed around the infernal realm of Abaddon, and so was born the arena.