The reasons we're here are:

  - By far the most popular use case of digital pens is drawing arts on a computer. Often anime, sometimes 3D.
  - Wacom is the king for artists. They also still hold some patents btw.
  - Wacom is DEFINITELY NOT THE KING for note taking and other non-art purposes. Laggy, parallax is huge, API is proprietary, etc.
  - Due to above, both Microsoft and Apple tried to replace Wacom by various means with not anime art use cases in mind but not ruling it out completely, from buying Israeli startups to reinventing stylus. 
  - The situations up until here threatened Wacom enough that it started upgrading and fragmenting pen implementations.
  - The situations down to this line caused bunch of players to join into the game, further fragmenting implementations.
  - And that had caused bunch of incompatible pen implementations, with limited successes with various standardization attempts. And here we are.
  - And by the way, Wacom is still the king for most pen buyers.