I am not opposed

So I'm not able to provide the kind of proper citations that I want to here, but it looks like there are a few factors here. Most importantly, cereal grains have a very short growing season, which in some instances lets you get multiple crops from the same land in a year. More importantly, it massively increases your resiliency. Like, it you plant an orchard of walnuts or something, it takes a decade between planting and being able to actually harvest, by which time your community has starved or moved along if that was your primary source of food.

Of course potatoes and yams also have a fairly short season, and you do see yams come up as a staple in parts of Africa, for example. But the other big advantages cereals have are in preservation and byproducts. Grain will dry itself out and keep for a long time compared to most other crops, and can be ground into flour, fermented into alcohol, boiled and eaten as raw grain, etc. Potatoes don't keep nearly as well, going to seed a relatively short while after harvest. Additionally, the threshing process gives you straw in addition to the grains, which can be used as building materials, animal feed, and a variety of other things. Most plants don't lend themselves to that many purposes as easily, though this is hard (in my inexpert opinion) to judge correlation vs causation on. Did we find lots of ways to use straw because we were already growing grains and therefore had a bunch of straw leftover? I don't know and I don't know how to find out, or even if it matters on a broader scale.

However, one specific consequence of this contrast is that in 18th-centuey Ireland the absurdly complex chains of subdivided plots being leased by multiple layers of absentee landlords meant that for most Irish farmers maximizing nutrition per acre was vital for being able to feed their families on the meager lands they could afford to cultivate. This is a large part of the reason why they took to the potato so strongly when it was introduced, and in turn is part of why the same blight that had swept through all of Europe with minimal fanfare absolutely devastated the country. It's not the only reason, but it was a large part of setting the stage for what happened next.

Anyways, thanks for giving me an interesting question to research instead of doing any of the shit I actually needed to be doing.

It's because potatos are the best

Biodiesel requires oil and sugarcane doesnt grow as well in north America given the climate, plus there are farm subsidies. Places like Brazil do use it for ethanol though