I cannot answer why it would not be. Perhaps the link author or poster wants to generate traffic -- please ask him or her about that.
I can however answer why it is not insightful / of no value. It's not saying anything of any interest about "how to open a file in python" beyond "don't go against the instructions".
You can ask me directly. We are compiling this and other insights, because we found these issues hundreds of times in the Python code we analyse. Clearly, not everyone is aware of the problem that goes along with wrong mode strings, but even if you do, you might still make a mistake when changing them during refactorings. So I think it is good to be aware. Especially for Python beginners it is a good thing to know. Sorry, if this bothered you. We maintain also a repo on GitHub where you can share any of your your insights: https://github.com/quantifiedcode/python-anti-patterns