Because:

• Ruminants like cows repair our depleating topsoil via regenerative farming (our current approach of using petroleum-based fertilisers is not sustainable)
• A single cow’s life can feed a human for 1 to 2 years, compared to the many incidentally killed animals (insects, rodents, frogs, birds, etc.) during the growing and harvesting of crops, plus the destruction of entire ecosystems to create the mono-crop farms in the first place
• Humans need to eat lots of fat to be physically and mentally healthy, and beef provides lots of fat (the low-fat high-carbohydrate diets recommended by various agencies — starting with the US’s department of agriculture in the late '70s via the food pyramid — are making us sick, with once-rare diseases such as cardiovascular disease, diabetes, depression, and dementia now commonplace)