The King said:
I don't understand why most of the time there are mixted books on market (half background, haf adventures). Frankly it's good to have a sourcebook but gretaer to have some adventures linked to it so that you can exploit it fully.
I remember at the beginning with AD&D, we had almost no detailed settings but a lot of scenarios. Now the trend has changed (and this is also true with D&D) where the number of adventures is proportionally small to the number of sourcebooks.
It is simple economics.
Players will buy sourcebooks. Dungeon Masters will buy adventures.
You will therefore sell, at best, 1 adventure for every 5 sourcebooks you would sell. When the market was much larger (around 2,000,000 + in the early '80s), adventures were economical, because you could sell enough of them to make a profit. Today, the market is much, much smaller, and you cannot, in general, publish something that is exclusively an adventure and make it profitable.
Goodman Games does it, because they are extremely specialized and have sewn up their market. Troll Lord Game has only published two traditional adventures for C&C (Castle Zagyg is a sourcebook), so the jury is still out on the success or failure of those. Even WotC stopped publishing books that were just adventures. If you check the Necromancer boards, you will see that they are debating whether or not to continue publishing adventures, as the adventures they published through Kenzer & Company have not sold well.