There are a few theories as to why different meats are often compared to chicken. One explanation for this is that chicken is generally milder than other meats, making it the most common choice for comparison. Chicken is also mass-produced, which means the animals are bred for large muscle mass and slaughtered earlier in their lifespan. As such, they don’t develop the complex flavors that a wild animal would.
Another possible suggestion came from Joe Staton the Museum of Comparative Zoology. He explained that amphibians, reptiles, and certain birds taste more like chicken because of a similar “evolutionary origin.”