The second reason was that something like underground fights was not too high on the priority list for potential targets by the police since they would much rather crack down on drug and violence-related gang crimes.
The third reason was that the fighting events were very small parts of a much bigger whole that was just a smaller layer of a much bigger organization that was formed by many influences.
Targeting such a small fighting event would do no real damage to those who were behind the events themselves and who held even bigger events that were far more difficult to gain entry into.
The level of secrecy and rules involved in the fighting events became much higher the more high profile they were so it would be very difficult to make any further progress after targeting one.
Those involved would be capable enough to find out where potential leaks existed and would be able to restart the ordinary fighting events without suffering much of a loss.