It isn't this cut and dry. You can cross-check and verify, but still have blind spots (or know that the tools have biases as well), and so consider it still important to mention the LLM use up front.
Or, if you preface a comment with "I am not an expert, but...", it is not often about seeking to avoid all blame, but to simply give the reader reasonable context.
Of course, you are right, it is also sometimes just lazy dodging.
Because if they'd actually read the output, then cross-checked it and developed some confidence in the opinion, they wouldn't put what they perceive as the most important part up front ("I used ChatGPT") - they'd put the conclusion.