Personally, I prefer not to get surprise PDFs; but that's just personal.
A better reason is that linking to the abstract page lets you navigate easily around the arXiv from there, including to the PDF if you desire; but there is no 1-click way to get from the PDF back to the abstract. (Of course, it's an easy matter of address munging, but even easier is not to have to do the munging.)
A perhaps less satisfying reason is the same reason that one doesn't deeplink directly to an XKCD image, but rather to the XKCD page for the relevant cartoon: a courteous acknowledgement of the source.
These are fine but pretty idiosyncratic. HN doesn't have citation rules so the 'always' seems overstated. People linking papers are already going the extra mile for the benefit of others and we don't really need to berate them about how they're holding their generosity wrong.
I didn't mean to come across as berating, but rather as suggesting a better way to link. I hoped that 'request' and 'please' would set the proper tone, but am certainly open to better ways of wording it. I meant 'always' to indicate that I specifically wasn't just complaining pointlessly about the present case, but rather talking about future links; but I can see how it came across like the scolding 'always' as in a phrase "you always do this."
The PDF contains the abstract right at the top, along with full attribution, and often uses less bandwidth. In most browsers, selecting the title and first author then right-clicking "search" allows a user to find related material on the open web.
My personal preference is the PDF link.
Your request was perfectly polite, I was simply wondering what your rationale was for it.
Multiple people have said they prefer not getting surprise PDFs. Could you elaborate on why? It's never something I've ever thought about. PDFs open in the browser now for most people, so it seems like it shouldn't make much difference?
I was going to add that some people on slow connections might not want to download large PDFs.
However, in today's web, the html page with the abstract (one paragraph) was a 2.5 MB download, while the 15 page paper including a figure was just 800 kB.
In my particular case PDFs linked from hacker news (accessed through the nextcloud feed reader) end up in my phone's downloads, which in that way fills up with PDFs I only wanted to read once.
There may be more of a security risk with PDFs, hard to say though. This was likely more of an issue back when using an external program to view them was a requirement.
So people can determine for themselves whether they want to download the PDF, by reading the abstract first. This has always been a point of petty annoyance for me as well.
https://github.com/imurray/redirectify