So what is its purpose? Should it give the author and audience a sense of belonging to the online world? Dissociating from people not belonging to the online world yet ("Neuland", anyone?). Just using it for teh lulz? Making things sound informal or less serious?
My experience is that I perceive articles preceded with 'Summary' instead of 'tl;dr' as much more no-bs-ty.
Edit: "Neuland" is referring to Ms. Merkel's "The internet is uncharted territory" comment by the way.
Slang is usually not about new meaning, it's about new 'nuance'.
Either making the same meaning fresher (by using a more modern term, which will get out of fashion after some time), or conveying an added nuance about the same meaning (the same way "Yes, I'd like to" and "fuck yeah!" mean the same thing as answer to the question "Should we go to the beach", but give it difference nuance, e.g. excitement).
That got shortened to "TL;DR"
Then it got adopted by people telling the stories to head off criticism and provide a soundbite version of the story. Basically, here's the whole story if you want, but if you thought it was too long, here's the gist.
Yeah it used to be that, years ago, but like everything getting popular, most of the time the initial meaning evolves or gets lost
[Citation Needed].
I'd also argue it's new and internet based.
Scientist have 'Abstract' because they need it.
The general public simply did not publish pre-internet. Now they do. So needed a new word.