Look at the name "Dungeons & Dragons". It combines two words: one for an underground location with medieval overtones, the other for a mythical fantastic creature, specifically one associated in legend with treasure troves. Games of D&D do not necessarily have to occur in dungeons or even necessarily underground, nor do they need to have dragons, but this short name does seem to convey the concept of what D&D is about: treasure-hunting in a setting straight out of myth and legend. There's also the catchiness factor, based on a combination of alliteration and brevity.
"Tunnels & Trolls" and "RuneQuest" are pretty effective names, for similar reasons. The Fantasy Trip doesn't really have quite the same power, although it does at least tell you what the game is about: fantasy, which at the time of its publication conjured images of Conan and Tolkien, combined with the idea of some kind of trip. There's no alliteration, but there's another rhetorical trick: a dual meaning to the phrase "fantasy trip". It's also short.
Of the retro-clones and other simulacra, Labyrinth Lord and Swords & Wizardry currently seem to be the most popular, or at least get a lot more mention and support; I think it's because both are pretty good names, based on the above principles. Castles & Crusades gets some interest, but maybe not as much as its fans prefer, perhaps because the name doesn't suggest "fantasy" as much as it suggests "medieval". Basic Fantasy Role-Playing Game oftentimes gets forgotten, possibly because, although the name is pretty blunt, it's not as short, catchy, or evocative as Labyrinth Lord or Swords & Wizardry.
So now I'm brainstorming names. Here are some I've rejected:
- Crypt Creepers (or Catacomb Crawlers, or remixes of those two): reasonably descriptive and evocative, but it lacks something and sounds too much like a creature name. Also, the abbreviation is too nondescript and likely to be confused with C&C or some other game. The second one has too many syllables for my taste.
- Menace Master: Not too bad, but not quite evocative enough unless you know that Nethack is set in the Mazes of Menace. Also, it feels too much like a knock-off of Labyrinth Lord.
- anything with "Maze": it's a nice, short, evocative word, but between Mazes & Monsters and Mazes & Minotaurs, I think the word is overused. The same can be said for "FooQuest".
- Lairs of Legend: sounds more like a collection of dungeons than rules for exploring them. Also, the abbreviation would be LoL. I'm torn.