Worldwide, there are estimated to be 375 million people subsisting on a vegetarian diet. That is not billions.
Not all of those people are healthy. Many have severe protein deficiencies.
It's fine if you have the money to purchase a menu which provides all your types of proteins and nutrients from fresh vegetables and other sources. Many people in inner cities do not have that luxury - they are barely scraping by to pay the rent.
None of this has anything to do on whether the Bible states that meat should not be eaten. Numerous examples seem to indicate that, after the flood, there are still instructions on when and when not to eat animal flesh. Including fish.