Because it requires a lot of biological investment to eat it. It’s rough on teeth and requires rumination or similar calorically expensive techniques to extract much nutrition. We evolved in the opposite path and optimized heavily for easily digested foods. We then take it a step further and cook them breaking the difficult to digest parts into an easer to digest form.

Also we do eat grasses, but only their seeds and fruits. Wheat, maize, rice, and bananas are all grasses

Grass came later.

Grass is nutritionally poor. The reason we are smart in many ways is due to our varied diet. Even if we had evolutionary gone in that direction we would be dumber. Eating grass is a specialisation.

Also, we would not look like we do. If you look at the digestive track of a horse or a cow, you will see that they are longer. Carnivores have the shortest and we as omnivores are in between. Being an omnivote is a good thing and in the end, we can get more nutrition by hunting and gathering than by grassing.

Worth noting, while individual cows’ behaviour and preferences vary greatly, the time spent feeding and ruminating usually adds up to 4-7 hours a day. Our society would be were we are today if we spent 7 hours as a species eating grass in order to make ir worthwhile.

Evolution can only evolve so much within an existing animal especies in order to specialise or fit in a survival niche. Hence you so not see sea crabs that can fly or flies that live in the bottom of the sea.

The thing is that cows can’t digest grass either. They have an extra stomach along their oesophagus which is basically just a pouch where the grass goes in first. There are a lot of bacteria and they can digest grass. Then these bacteria grow because they eat the grass.

Then the cow swallows these bacteria and digests those. That’s where a cow gets their calories from.

There’s a reason grass is so common - it’s because it’s a wildly effective life strategy. Grass is actually quite hard to eat - there’s basically no nutrition in the leaves themselves, and grass evolved to incorporate silica “needles” in its leaves, so that it wears down your teeth when you try to eat it anyways.

Not to say that it’s impossible to eat grass, but you need to undergo a ton of highly specialized adaptations to make it possible. For most animals (including humans), it’s just not worth the effort

I’d rather evolve the ability to photosynthesize, now that we have indoor lighting. It’d save a whole bunch of time and grocery bills.

Take the tier zoo aproach. Would you rather use evelution points on grass or evolution points on being big brain.

Smarts required more calories.

All forms of grass:

• Corn
• Wheat
• Barley
• Rice
• etc

A lot of grass. Like lawn grass. Is wheat.

If you let it grow more.

So actually we did evolve to eat grass.

Cat grass is wheat grass.

Why? Because otherwise we wouldn’t exist and that wouldn’t be in line with the future.

Grass is mostly cellulose and lignin. Those molecules are difficult to break down.

Animals that can digest the cellulose either need a really long digestive track or to do something really gross to keep the stuff in their digestive track longer.

It’s more efficient to let others eat the grass, and then eat them

It’s all down to the way the brain works. Our brains use up something like 20% of our calories when standing still doing nothing.

Grass does not supply the amount of calories and micronutrients needed to keep the human brain running, simply because it is low on both of those things.

Grass eaters have multiple stomachs, slow digestion and graze pretty much the whole time they’re awake, and because their brains use a lot less energy than human brains, the balance works out.

Vegetables have pretty limited availability for protein, as an animal you have sit there eating grass all day. Our ways allow us plenty of time to be smart & stuff