I would say its to protect people, if you ask a LLM for a legal answer and trust it, then you could get into legal trouble when it turns out to be wrong.
Not only are LLMs wrong like ~1/10th of the time (for the more advanced ones) but law is also an area where there is black and white rules, but also there is interpretation of some aspects.
Some things are set in stone and some are about understanding the intention of the law and being able to back that up in a court if it was challenged.

Do you want the public trusting a LLM that says "oh yes you can claim a tax deduction for an Xbox because its for stress relief related to your job" and then you get whacked with a fine for incorrectly filing your tax.

Using a LLM to help your draft an email to your uncle = low risk. Using a LLM to help you decide if you actually need a medical procedure your doctor has reccomended = high risk.

I guess it's like banning loan sharks. Sure some people could only.get loans through them because banks were racist or whatever. But it's objectively bad for everyone using it mainly because when it's bad its really really bad.

law in itself is very gatekeepy - you have to learn the "correct" way to interpret the words and then get certified for it.