In the past, it was not uncommon for me to update Firefox, try to figure out why an add-on stopped working, and only then realize that the add-on in question hadn't been maintained for more than a year.

If the maintainers of ABE really want their users to switch to uBlock, they could push a final update that displays a notice about its own deprecation. There's no need to rely on the app store to do that.

But they're not doing it, and I suppose it's because even without further updates, ABE will continue to work perfectly fine for the foreseeable future. In fact, according to the article, it will work even better than before.