EDIT: Comr to think of it this was the problem with APNG trying to replace GIF. Everything supports GIF, no one supported APNG (relative to GIF) so it never really gained traction.
Even though 75% of users have a browser that supports it the format has no mindshare so no one uses it.
I think that the creators of PNG being against it and saying we should all use MNG instead didn't really help. Not to mention the fact that it took ages for plain PNGs to be supported by browsers.
To be fair I’m only vaguely aware of APNG. I thought it was called PNGA before I looked it up to see what browsers supported it for my comment.
I also had a no-name digital camera that inexplicably supported JPEG2000.
Other than that, I’m don’t think I’ve seen it much in the wild.
It is also used for digital cinema distribution. It was chosen for that role specifically because it was not in widespread use.
To be fair, the same was true of the original JPEG when it was released. JPEG also has an optional arithmetic coder based on IBM's Q-coder, which was heavily patented at the time. To this day, no one implements that, even though it does improve the compression and even though IBM's patents have long expired.