Because they are trying to sell the idea to the western countries. But macroalgae culture is a standard business in China and Japan since thousands of years.

I had eaten it, the green are good, salty when fresh and a little bland after cooking it, the red are a little bitter with a medicine aftertaste. You should use it sparsely in kitchen. Is more a spice than a main dish.

The main problems are that climate change removed 90% of the Laminaria forests here in the last 20 years and that the red algae are harvested and sold for pharma and industry, so aren't really available to harvest to the common people. You need a permit for this. The culture is also complicated here.

"Seaweed" is a rather ill-defined term in English that regroups a lot of different algae. Nori is made from red algae, that are included under the term seaweed.

Seaweed is a very confusing term, yes.

Should be used for marine weeds [upper plants with flowers], but the term refer to algae that are a different category. Some algae are plants. Other are neither plants, animals or fungi and have their own category.