My two cents: Directory Opus has been around since the 90s, and possibly before - though I consider "DOpus proper" to start at 4 or 5. I was introduced to it with Magellan (DOpus 5.5) on the Amiga and immediately loved it.
Even in those days many people preferred DOpus 4, as it was more like a traditional file manager of the Midnight Commander mould (though DOpus 4 predates it and indeed MC probably copied DOpus). Many couldn't be bothered to configure DOpus 5, despite its incredible power even then. While I used it for practically everything you can think of, some people just wanted to copy files from one folder to another.
Once I gave up the Amiga, I knew DOpus was available for Windows, but I never gave it much thought until I bought version 11. You see, Amiga Workbench was very limited. Directory Opus gave it features that most people take for granted, basics like pattern select. Windows Explorer, I felt, was "good enough" otherwise, and I had no need for DOpus. Absolute idiocy on my part, in blunt hindsight.
Then two years ago, I had a job where I had to juggle a lot of different projects scattered all over a business intranet and in various numbered folders on a laptop hard drive. It was a nightmare. Then some random nostalgic thought came to me, "I wish I had Directory Opus like I did on the Amiga". So sure enough, I had a look again, and found it was even better than I remembered, and boy did those tabs and USB dongle mode look PERFECT. And indeed they were. I've never looked back. Even at home, I don't think I could ever go back to Explorer.
So yes, while I'd agree with you that DOpus' two real weaknesses are (and always have been) advertising it to people who have no idea what a real file manager can do, and convincing people to do more with a file manager than the basics, it has existed for a long time so it must be getting something right. And long may it continue.