This is the main thing that immediately tells me something is AI. This form of reasoning was much less common before ChatGPT.

I don't think this is true. The LLMs use this construction noticeably more frequently than normal people, and I too feel the annoyance when they do, but if you look around I think you'll find it's pretty common in many registers of human natural english.

And each of us has patterns. I bet if you read a million of my posts, you would be annoyed with my writing idiosyncrasies too.

Yes, this is absolutely part of it, and I think an underappreciated harm of LLMs is the homogeneity. Even to the extent that their writing style is adequate, it is homogeneous in a way that quickly becomes grating when you encounter LLM-generated text several times a day. That said, I think it's fair to judge LLM writing style not to be adequate for most purposes, partly because a decent human writer does a better job of consciously keeping their prose interesting by varying their wording and so forth.

Not sure what the downvotes are for -- it's trivial to find examples of this contruction from before 2023, or even decades ago. I'm not disagreeing that LLMs overuse this construction (tbh it was already something of a "writing smell" for me before LLMs started doing it, because it's often a sign of a weakly motivated argument).