The reality is combat sports have been popular for many 1000s of years. Before the romans and after. Certain forms of wresting were incredibly popular in the past. The amount of people that watched or listen to major historical boxing fights is crazy.

To hold up Roman as some sort of maxima doesnt really hold up. Its just that they were rich so they invested more in spectical, just as we do now.

The one change that has happened is that animal fighting and baiting has become unpopular and unacceptable over the course of the last ~200 or so years. It's not 0 but there's much less dogfighting, cockfighting, bear-baiting etc