This may seem an odd question, but how come the page for the Catacombs Pack doesn't mention that the Gamer's Edge sampler disk for Catacomb also includes Dangerous Dave?

Probably an oversight. Potentially an intentional omission in order to keep the product description focused on Catacomb / to avoid confusion that Dangerous Dave might somehow be a part of the Catacomb series?

Whatever the story may be, I don't think it would necessarily help boost sales for potential buyers to know that they'd be receiving a [pretty lousy] DOS-era platformer as an addition to the collection. Probably wouldn't hurt sales to mention it either, I guess.

I think the first Dangerous Dave is freeware anyway so it's not a big deal I guess.