It's not one thing in particular, it's woven throughout from the structure and phrasing to the design and color choices, there is this general vibe to claude produced artifacts. Part of the problem is that so many people are using claude, we just see this more and it's become tiring, so even a modest amount carries more impact than average.
If you want humans to spend time reading and evaluating, put the human time into writing and editing.
If you want humans to spend time reading and evaluating, put the human time into writing and editing.