Half of the agricultural land in the US is suitable only for grazing, not for cultivation.
And cattle are the only food animal that can thrive purely on grazing. Pigs, chickens, etc, need supplemental feed.
Cows grow on grass. Even grain-fed cattle spend most of their lives on grass, only sent to feed lots for their last couple of weeks.
Eliminating beef would seriously reduce our food supply, because contrary to the usual green mantra about how it takes x pounds of plants to grow one pound of meat, and it’d be less wasteful to just eat the plants, this is only true if the plants are something we could eat. In the case of cattle and grass, this isn’t true.
And then there’s the simple fact that pasture is far less destructive to the environment than row crops.
How about sheep? Though we don’t much like to eat mutton.