system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do so few plants make up so much of our food?

There are 50,000 edible plant species but only 15 make up 90% of the food we eat (excluding meat). Why is that?
gpt
Plants do this thing where they convert sugar to cellulose in order to grow. We can't digest that because we don't have the enzyme to convert it to sugars again. The plants we do eat have been cultivated over thousands of years to select for the best crop possible, and these plants tend to have a lot of sugar in sugar form like fruits, or in starch form (which we can digest back to sugar) like root vegetables. 

We've basically "domesticated" plants so that they're starchy and sugary, and recently, look pretty and big as well. The plants we don't eat are high in cellulose and not much else. Also, plants that we don't eat tend to be difficult to cultivate or only grow in specific environments that can't be brought elsewhere.

Potatoes and corn? You can grow them anywhere.