I once made compost out of only grass and a bit of paper. It sucked, but the compost made out of leaves looked a lot better and darker

I also noticed that it's much easier to burn wood than bamboo (a grass)

also when I look at leaves, they look like a web of cells, and seem like they'd be easier to digest than grass, which looks like a line of cells that are all coherently arranged in the same direction

pic related, a grass-like organism