Fallout 3 Message Board  

When Oblivion came out, it used practically the same mod making system as Morrowind did, so people didn't have to re-learn how to use it. Fallout uses a different one, The GECK, and people have to learn another method. Oblivion has also been out for about three years and Fallout 3 hasn't even been out a year. Give it some time and there will be loads more.

also i don't believe bethesda made people wait so long before the release the construction kit for oblivion like they did fallout. still don't understand why they did that

Because when they released it with Morrowind, the game was already modded to hell and gone before any patches were released and this created a PR nightmare with thousands of people posting on Bethesda's forums about how the patch broke the mods and the combination corrupted their install.