Have you ever tried to communicate in beginner/intermediate-level German with a German speaker? They'd most likely insist on switching to English.

It's a natural reaction in one-on-one conversations to switch to the language that least impedes communication. That's annoying when you're trying to learn a language but wouldn't be too bad as an outcome if your actual problem is just the lack of English documentation.

But in the case of a larger online community where German is used by default, you'd be unlikely to get everyone to switch to English just by posting in bad German. After all, you might just as well be a Kazakh whose English is even worse, and as just another anonymous newcomer, there's no reason to accommodate you in particular.

OP brought up English because it’s one of the most widely used languages in the world, thus a translation would make KNX more accessible to everyone. Standards are created to make things interoperable across manufacturers so expanding the market to include other countries ( and competitors) is good for consumers everywhere. Unfortunately German isn’t as far reaching a language and asking the majority of inhabitants in other countries to learn it may be too high a barrier to entry

After many attempts to speak german with germans, it seems to be a consistent theme that they prefer english if you are incompetent.

Not everyone has the time to learn yet another language. Besides, learning a language to understand content like this takes a lot of time. (I speak 4 languages already.)