You don't hear much about cartos because they are very early technology that was refined, and hasn't changed at all in a long while (I would like to see some with cotton or rayon filler, though, and perhaps a bit better airflow!). Likewise for carto-tanks - there's not much to them, so there isn't anything to improve on.
Despite that fact, they're reliable performers, perhaps the simplest types of heads to use, and many folks really like them. They just don't get much press, because there's nothing new about them.
I do worry a bit, though. As an example ecigsupply recently dumped all their boges (99 cents for a 5-pack! they ran out pretty quickly even though they still show them on their sale page). And although I've only been to a couple of B+M's, I've never seen a carto setup at any of them - their "low end" is something like evod tanks.
If they're dying out, it's from the supply side, I think - fewer new vapers are introduced to them, so they aren't seeing the sales growth that other types of gear have. (Plus, they're hard to distinguish from the crappy gas-station cigalikes because they look about the same).