In these past millennia the development of our consciousness and mentality is often overshadowed by the evolution of our physic. The wars the we experienced over the course of time have shaped our ethics or morality as a civilization. Compared to 500 years ago, I think that the current population can empathized and appreciate life more.
One of the most sensitive issues or topics to discuss about sports are those involving animals. Horse racing is very popular spectator kind of sport in almost all parts of the world, bullfighting on the other hand have become one of the most iconic events that represented Spain as a country.
Although it is not a baseless accusation to refer to sports involving animals as unethical we can also not deny the fact that this is already ingrained in our society for far too long. Horse racing could be considered as one of the most ancient sports with evidence that can be traced as early as 4500 B.C.E. in the central plains of Asia (yeah Genghis Khan, and most popular leaders with Khan in their names LOL) and there are also a separate evidences that horse racing (also with carts) had been a popular sport for the ancient Greeks. Some more 'brutal' sports involving animals like cock fighting has traces in the Mayan civilization. The bottom line here is that sports involving animals already assimilated in our culture even until now. When something became part of a culture or tradition then it's very complicated to alter or neglect it. If you deprive the Chinese to use chopsticks or Filipinos to eat rice in their entire lifetimes then that will be infinitely close to impossible.
Another factor that hinders morality in this sensitive issue is the economy. With no exception, any kind of sport gains popularity with money as one of the biggest driving wheels. Teams in NBA cost billions of dollars and that's just the tip of the iceberg if you consider all assets that can be related for every kind sport. Sport betting or gambling is one of the most influential elements that make a sport alive. We as humans love to take risk and the feeling of being triumphant against certain odds is a very addicting feeling. And business owners love to play with these emotions to make even more money. It's a psychological trap that is very difficult to escape.
The truth might be hard to swallow for others like the vegetarians, animal advocates and some religious groups but the facts are already laid on the table. Sports involving animals can be minimized but I think based on our current state it is still impossible for total abolishment if there would be any attempt.