It's quite similar to the proliferation of code editors from 2005-2015ish. For a while, practically every language had its own IDE (for me, I remember using HaXe and FlashDevelop). Then, editors like Atom and Sublime came along, raising the bar. For the past five years or so, seems to be the default. The excellent extension system allows people to worry about features, rather than re-creating the IDE.
When it comes to note-taking, I expect the same thing to happen--we just need a good, open-source foundation. I fully expect that the winner will be a wrapper around ProseMirror [1]. See also ReMirror [2]