For a while now, people have been expressing concern about Chrome’s dominance creating a browser monoculture. With Microsoft’s recent switch to Chrome, the choice of rendering engine was effectively reduced to Blink (Chrome), WebKit (Safari) or Gecko (Firefox). Whilst there are a large number of browsers for desktop and mobile users out there, almost all are based on Blink/Chromium.
As well as displaying web content, HTML browsers are used in a wide variety of products for application and user interface rendering. The potential effect of one company dominating the implementation of the standards is that they are biased towards web page rendering, their largest use case. Focusing solely on web content could limit the wider appeal of HTML.