Various plants (dark leafy greens/cruciferous vegetables) do make up the foundation of a healthy diet, but do not provide significant protein or fats. Meat is very useful from a dietary perspective. You can make a quality vegan/vegetarian diet, but hitting high protein goals for those who are active can be difficult. The majority of vegetarian+ protein options are also high in carbs.

Plus, meat is tasty. It makes perfect sense people look forward to lab-grown variants that are ethically sourced and have no adverse health effects.