This is a great question. In order to understand the glories of fighting in the amphitheater, a little historical context is important.
First, we need examine who these gladiators were. Most of them were captured soldiers. This meant that they were slaves. And if we look at the life of a slave in the ancient world, we would realized that their lives were not very promising. By knowing at this perspective of the ancient world, anything would be a welcome change for slaves.
Second, during the time of the Flavians, there was a slight shift in Roman culture. Some historians call this period a period of "bread and circuses." There was a culture where people loved entertainment. There was also a rise in popularity in gladiatorial combat. The Flavian amphitheater is a case in point. Hence, there was great glory to be had in the arena. In other words, gladiators could gain enormous fame and wealth, which was something that was not open to them as a slaves.
Finally, the ethos of Roman culture was warlike. Men distinguished themselves in combat. So, it was natural for men to fight.