Why is Ethernet so popular?

Answer 1

It's always been cheap technology, for a start. Many years ago IBM's Token Ring cards were 10 times the cost of an equivalent Ethernet card. So companies started to use the cheaper technology as it achieved exactly the same end result as the more expensive technlogy, and it became the standard. A bit like how VHS swamped Betamax.

Then once a standard develops and the vast majority of people use it, economies of scale means that it becomes cheaper and cheaper to make the kit, and you can sell it for less and less, making it even more attractive to buyers. And as it makes more sense for manufacturers to back the popular product, most development efforts go in to improving that product. That means that competing architectures got left behind and eventually died out except for very specialised applications.