Nutrition is something that you need to think about. And yeah, people don't do it right most of the time.

That's the thing though, you have to devote way more time and energy to designing a balanced diet. And even then, depending on where you live, it can take even more time and effort to actually find the food you need. Outside more urban areas, vegetarian-friendly restaurants and markets can be scarce. Your nutritional considerations become a major part of your life, and most people just don't have time for that.

But that's not the only thing, there's the social aspect. Eating is very frequently a social activity. Cutting out meat makes it much more difficult to engage in communal meals, be it restaurants or potlucks. On top of difficulty in finding good options, there's the unspoken tension that being a vegetarian around people actively eating meat creates, especially in meat-centric contexts like barbecues or Thanksgiving dinner. The social difficulties can make it too alienating a prospect for most people.

I get it, but it's just not rational to expect the majority of people to cut out meat. I've tried.