One has to imagine a future where one of sevetal things happen. Two possibilities come to mind.

1. The government somehow bans beef, chicken, turkey, etc. This, I can’t stress this enough, will not happen. The backlash would be massive and leaders would be out on their ass swiftly and the decree reversed.
2. Climate change and animal flus render meat so expensive that it escapes affordability for the average man More catastrophic, but also more likely. IMO average folks go largely vegan at that point, meat becomes a special occasion thing for them.