even if it was too complex people can teach them selves with lots of time, effort and trail and error. Many systems are dubbed "Complex" but after time and people getting there hands on it and using it, it doesn't become that complex to many. Also Modders are mainly students studying computer science, computer programming or a games course and people who have some experience in computers development or a really patient and eager to learn person.
I dont get why they dont come out and say "The reason we are not doing mod tools is because we want to sell DLC which people may not buy when mods are avaiable".
Which is a valid but flawed point because people will buy the DLC over mods for several reason:
1. They are on the public servers
2. There are always enough people any time to play them
3. They are of very high quality compared to the average mod.
People will buy the DLC even if there was modding tools avaiable and you can always state that you cannot copy DLC maps or get banned.
Of Course That's Just My Opinion, I Could Be Wrong