At the start of the Neolithic, besides barley, 2 species of wheat were domesticated separately and they evolved through domestication into einkorn wheat and emmer wheat.
Einkorn wheat has always remained a minor crop, while either barley or emmer was the major crop, depending on soil and climate. For instance in the early Ancient Greece barley was the most important, while in the early Roman Republic emmer was the more important. Later, emmer ("far" in Latin) was mostly replaced by durum wheat ("triticum" in Latin), and even later durum wheat was mostly replaced by the hexaploid bread wheat ("siligo" in Latin).
Besides the original emmer and einkorn, other wheat subspecies have appeared many thousands of years later after domestication, either through mutations, like the tetraploid durum wheat (pasta wheat) or through hybridization, like the hexaploid bread wheat (and also the hexaploid spelt wheat).
Why is that? I thought nitrogen is taken in through the roots, then distributed as other ground-based nutrition, regardless of the height.
The main thrust of modern crop breeding has been to create crops that you can successfully get to harvest under high-nutrition environments, without it literally falling over or succumbing to disease due to the turgid, fleshy growth. Even then, if you're applying more than maybe 150kgN/ha, you will be relying on plant growth regulators that inhibit auxin/gibberellin response to keep the plant under control.
In the article it describes the crops as more drought resistant etc.
As in all things commercialized, the tempting easy path weakens in the long term. Mono crops are easier to grow and then the soil gets depleted beyond all recognition. White bread probably outsells whole wheat in America but it is basically devoid of nutritional value.
“Old” means things were scarce because people had to work by hand and oxen. So a failed crop meant a dead family.
White bread is also one of the cheapest sources of energy, though depending on the geographical location either maize or rice may be slightly cheaper sources of energy, but which provide much less protein.
Among cereal products, wheat bread has the highest protein content, except for oats, but oats are much more expensive per protein content.
If you eat white bread in preference to any other starchy products, like those based on rice, maize or potatoes, this ensures a higher protein intake per a given calories content, which enables a lower consumption of more expensive sources of proteins, like those based on legumes or on meat.
White bread cannot be the only food that one eats, because other kinds of foods must provide other nutrients, but it can provide at a minimum cost major fractions of the daily intake of proteins and energy.
After experimenting with many different healthy diets, I have settled on a variant that I consider optimal, where wheat bread that I bake myself at home typically provides about a third of my daily protein intake, so its nutritional value is quite important (and the fact that it is very tasty is a welcome bonus).
Oat however is from the tribe Aveneae.
Nonetheless, these minor varieties of wheat have remained important due to their ability to grow in soil or climate conditions where the more productive modern varieties of wheat fail.
So they were frequently used as "backup" crops, for the cases when bad weather or pests destroyed the main wheat crops.
As said in the parent article, they may become again more important where soil has been made worse by modern agricultural practices.