Because using LLMs for legal work has never gone wrong, and LLMs have never cited completely hallucinated cases
I use AI extensively in my legal work. But I check every citation myself, manually. That means that I read the entirety of every case that I plan to cite in my output, and I check on Westlaw that it hasn't been overridden by a later decision. If you're just producing the AI's output verbatim, then you have only yourself to blame when things go wrong in the courtroom.