From a dev point of view providing official modding tools is a bit of a nightmare. When you provide official tools you add a whole other layer of needed support and the game design is actually more complicated as you need to leave various hooks open for that modding support.
By allowing modding to exist they give the community the options but even this creates headaches. You see on forums, players begging devs to make mod A work, or why does Mod B not work.
Now if they wanted to do an adventure creator, THAT would excite me, allowing the players to create more real content. Even that however can be a nightmare from the dev side and lets not forget the whole mess of they have to license this crap from Hasbro.
