And yet another slight different angle, in case it helps :-) Sometimes you feel strongly about a topic and so when you write about something that tangentially refers to it, it is very tempting to express that reference. Unfortunately, if
you feel strongly about it there's a good chance that others also feel strongly in the opposite direction. The result is that you distract those people from the main reason you wrote the text.
Or in other words, you get on the front page of HN and the first 20 or 30 posts are talking about social justice warriors and not how to provide good exit experiences for users :-)
In a different, but similar way it's easy to miss your readers when talking about technical subjects. For example, if you have a very deep insight into a technical matter, it's often difficult to understand why your readers don't understand what you are talking about. The trick to good writing is to approach your reader on their terms and invite them in. If you can explain something in terms that they relate to, then suddenly they can understand it, whereas before they couldn't. It's easy to think that the reader is uneducated and that's why they didn't understand. However, it is the purpose of the writing to educate the reader.
In the same way, you might think that the reader should not get distracted by an offhand comment. It might be easy to fault the reader for not being able to see it in the context that you see it. However, just like the uneducated reader that can't understand a technical topic, you can't expect your reader to understand your context without a considerable amount of effort to set the stage. As it is not the main topic of your thesis, it becomes a bridge too far for the reader and they miss your point entirely.