[ashark]

I think it's a reaction to lawyers posting "I am a lawyer; I am not your lawyer; this in not legal advice", presumably as some part of explicit or implicit professional ethical or legal obligation, plus the typical "IANAL" disclaimer that frees the poster from a bunch of wasteful hedging and qualification in the rest of their post by setting expectations at the beginning. It's the reasonable "IANAL" merging with negation of the maybe-also-reasonable disclaimer actual lawyers use, to form a less-reasonable mix of the two.

[EDIT] probably also part of a US thing about constant over-disclaiming and posting rules/regulations everywhere, which I gather is really weird and makes us come off as kinda repressed from the perspective of people from other countries, even those from the more repressive variety. I don't know, I'm American and going on the reactions I've read of foreign world travelers to Americans' love of basically-useless posted quasi-legal language on seemingly every flat surface, and poles where flat surfaces aren't available.