I've seen this a number of times, though I can't remember a recent example.
One site attempted to do it more intelligently, and the footer floated via z-index and pinned to the bottom of the window such that it was always visible despite the infinite scroll. Though they got it a little wrong and didn't account for the footer height in scroll calculations so if the content wasn't infinite so you could get to the end of the scroll, the last couple of lines were obscured by the footer. There must be quite a few ways to do this “properly” and smoothly (just thought of a couple right now, and I'm no front-end guy), assuming you consider automatic infinite scroll to ever be considered doing design “properly”.
It’s not a hard problem to notice or fix, probably just comes from people not using their site a lot. All you need to do is insert your content in a fib before a final “filler” div that has the same height as the floating footer. If your floating footer doesn’t have a fixed height (and there is some really good reason for that) a further hack is to measure it and then set the height of the filler div in js.
Also works well, but that might introduce janky behavior with iOS safari’s title bar and tapping the top to scroll to top in my experience. I don’t know if this has been fixed, it’s been a while since I wore a CSS hat, but I vaguely remember fighting with mobile safari and overflow divs a lot.
Not exactly the same, but theverge.com has recently decided to shove about 50 Outbrain ads, across 3-4 loads, in between the end of the article and the comment section. It makes me livid every time, yet still I go back :(.
I'm fairly convinced sites do this because someone there is sick of having to moderate their comment section, but doesn't have the buy-in to get rid of it entirely. So instead they stick a bunch of ads above it, hide it behind a button, etc. in hopes of annoying people into not commenting.
Try to read the text or click on a link in the footer, and if you're lucky the request will be slow enough.