One issue is that it can be leveraged to maintain a monopoly. Microsoft famously made a bunch of small modifications to the HTML standard, so that web sites that wanted to work with MS Internet Explorer had to write custom versions to be compatible. But because so many people just used IE because it was bundled with Windows, those “extensions” started to become their own standard, so that then other browsers had to adopt MS’s idiosyncrasies in order to be compatible with the sites, which in turn harmed standardization itself. They even had a term for this technique: “Embrace, Extend, Extinguish.” It nearly worked for them until Google pushed them out with Chrome. Microsoft tried to do the same thing again with Java until the government got involved.

It’s complicated, certainly, but there are legitimate cases where “just a little tweak” can be quite a big problem for a standard.