The attraction, especially for a setting encompassing a lot more than what has already been covered, is that it is still being supported. That means other people are still working to increase the scope of my campaign setting. If the support stops, I might as well have designed my own game from the start, since I will have to do all the remaining work myself anyway.
This still makes no sense to me. Would you rather play Mongoose Traveller right when it starts, when just the core game book is available? Or, after the game has been established, when a third of the material is available (say, 3-5 years into the game's production life). Half-way through, with half the total books?
Or, would you rather play Mongoose Trav once EVERYTHING is out?
If I had a choice, I'd go with the last one*.
*of course, there are several other factors that go into when to play a game. Desire to play is paramount, and, I agree, the "heat" is on when a game is being heavily marketed and seems "new".
I came to Mongoose's Conan RPG late, just a year or two before publishing stopped. And, I'm glad I got into the game then rather than in the beginning? Why? Well, I started with the best set of rules. Mongoose Conan went through three editions, and I started with the latest one. Also, I could see all the supplements that were made, buy what I wanted, and rock-n-roll from there (I ended up buying the entire game, and I got a lot of it at close-out costs as the word spread that it would no longer be published.
Clearly, imo, I'd much rather play a completed, established game than get in on the beginning when it could be 10 years or more (for a popular game) to see all the supplements.
--which is why I wonder why someone would rather play a game that is "in print".
EDIT: The only "effect" that I find different with Mongoose Conan is that not too many people want to talk about it. It would be fun to talk about some aspects of the game, but it's a niche game with, I guess, not too many followers. If it were "in print", there'd still be people at the Mongoose forum talking about it. But on the other hand...how much does that really matter? I've got may campaign, and we're enjoying the heck out of it.