Basically OS developer dropped the ball. Internet caught them by surprise and few decades is apparently too short for them to come up with new appealing abstractions to fit the new environment. So browser developers took over and did just that.

Same way webdevs ate desktop app dev's lunch because they had no idea how to innovate on decade old ideas.

To sum up, no matter how well you are positioned for something on paper, if you won't do it, someone else will.