They're wonderfully convenient and if I had one I doubt I'd give it up - I was always jealous of a friend that did. But it's fair to say they aren't AS efficient as modern stoves with true secondary burn tubes. Not all secondary air supplies are the same. I'm not saying they're bad, just agreeing that you might get 10% better with the latest designs. Still, very convenient...
Two more reasons they probably went out of fashion:
1. A lot of people are installing inserts these days, and stove makers are coming out with a lot of models that can be set up both ways with the right leg/trim kits. But you can't use a top-loader as an insert.
2. They're... not the most BEAUTIFUL of appliances, are they? It's a great hunk of black iron. People are burning less wood these days and doing it more by choice - not everybody, but more people anyway. You see a lot of really decorative stoves with beautiful glass doors, enamel finishes, wrought iron inlays, etc. Even my basic US Stove insert that I got for my living room for $1200 has a lot of nice detail on a nice glass door. You go to any wood stove dealer these days and you won't find any utilitarian models, it's all QuadraFires, Osburns, and Vermont Castings - and they're all as decorative as functional. Heck, a good soapstone stove runs $4k-$5k. They must be selling because they're still in business, so I figure people are just willing to pay a bit more for something nice.
I still like my Jotul 118 with that decorative scene on the side. But I think cast iron is pretty as-is. I guess not everybody agrees.