[dragonwriter]

Practicing law without a license is an offense in many jurisdictions; providing legal advice is in some cases within the scope of legal definitions of practice of law. (For people in certain roles outside of but around the legal profession, even implicitly holding oneself out as a lawyer or person qualified to practice law may have additional concerns.)

While public comment for which no one has been charged money may be outside of the bounds of what would be covered by most such laws, some people view it as best to be clear (and, in any case, such a disclaimer served as meta-legal advice that the matter at hand is one on which you should consult a lawyer if you have critical concerns.)

And, there are other concerned for lawyers in communications that might be mistaken for providing legal advice.

All that combined to justify disclaimers that include some or all of, as applicable:

I am not a lawyer.

I am not your lawyer.

This is not legal advice.

(Incidentally, I am not a lawyer, I am not your lawyer, and none of this is legal advice.)