The reason is stated towards the end: > In general, any laxness in actual implementations of a system can create a similar spiral of de facto requirements. Th

The reason is stated towards the end: > In general, any laxness in actual implementations of a system can create a similar spiral of de facto requirements. Those "de facto requirements" mean that writing something simple becomes inordinately complex because noone fixes broken clients. And you can't test changes because you don't have access to these broken clients. It also leads to nasty bugs. For example, if you ignore extra parameters and provide defaults for others, now a misspelled parameter will silently fail. The best example is how hard it is to write a browser. The standards are very complex, but it's magnified by the complexity of supporting "real," namely broken, HTML and CSS. That's contributing to the browser mono-culture.