In the case of Reddit, probably when you click interesting thing your current url is saved to history and then you go forward, you go back the url is used to construct page again, but that url probably represents a concept like "Currently most popular posts under subject X" not what lifeplusplus was just looking at with particular offset etc.
Regarding not making the back button do anything in certain cases, I think part of the problem is the shitty infinite-scroll, endless toilet-paper UX that many modern apps use for pagination. It makes a lot of UX choices awkward.
Say you're building some Instagram or Pinterest type of App and you just have some kind of endless scroll to view content continuously. The user scrolls for 10 minutes seeing 100 pages worth of content on one root URL, and then clicks on another page and then goes back. What then? Do you put them at the bottom of the 100 pages on the original page after they hit that back button?
It's not super difficult to save say the last item you scrolled to and go back there when you reload the page from a back button press, but that specific UX just makes it awkward to know where you even are within a specific page. Maybe if people get lost when going backwards and that's the UX choice, it's not even worth bothering.
You could easily use unique encodings of URLs to restore the deep state of the website's content. Even when you would use e.g. only the #hash like the old twitter app did.
[1] https://developer.mozilla.org/en-US/docs/Web/API/History
Is the Internet full of idiot engineers at LinkedIn etc?
I humbly submit it is not easy, these days, to deliver well-behaved SPAs.
PMs have never cared about it in my 20+ years of experience.
Did you believe otherwise?
The cure to Impostor Syndrome is to realize that we're all impostors. Might as well get in on the action and put that Peter Principle to work.
The evil marketing side of me says, bring up a dialog-box;
"your time is important to us,
would you like to view a 15-sec sponsor-commercial and return to your-position on the previous page Yes/No"
'Yes' runs the Spot and returns to the exact position on the previous page.
'No' either just removes the dialog-box, and/or takes you to the top of the current-page,
or takes you to a random-page very loosely related to the subject of the previous page.
P.S. Please don't Kill ME!I know HN doesn't have this problem, but I still do it out of habit, and I then open multiple submissions of interes and go through them.