Mary Beard has some additional observations on the Chester amphitheatre buzz, and I found myself nodding to this excerpt:
"But my main argument was that historians and archaeologists, as well as journalists, have wildly over-estimated the importance of gladiators in the ancient world. It’s us who is obsessed with the arena, not (so much) the Romans...The inhabitants of Roman Chester would have been lucky to see a handful of B team gladiators twice a year. The more interesting question for us is what went on in these amphitheatres on the other 360 or so days."
I think this rings true, but on the other hand, we wouldn't make such a big deal of the Super Bowl (the annual American football championship game) if it were held on a monthly basis. Infrequency doesn't translate to a lack of interest, and it may have had the exact opposite effect, ensuring that the place was packed to the rafters with excited fans when those poor B-team gladiators filed in.
ETA: Tony Keen correctly points out that in any event, gladiator fights played second fiddle to the chariot races.