There are a couple of things that may be contributing to the lack of “self-activation”. Problems with “Executive Functioning” or being able to think of what to do or how to approach a task are common. Problems with “Working Memory” are another cognitive area that may be causing the difficulty.
Then again the task just be boring and tedious which cause ADHDers a great deal of pain from the strain of trying to subdue their attention and concentration to get that boring chore done. Yes, my desk is a mess, cleaning it up is boring and answering this question is a lot more fun!
In reality, ADHDers have the same problems as neurotypicals, but the disorder makes it very difficult and very energy consuming to “just do it”. So, to actually get going ADHDers have to use techniques above and beyond what normal people do. This can include breaking the task into smaller pieces, setting up rewards for completion, identifying personal pay value of the task and other goal setting methods. It may seem more involved and unnecessary but to an ADHDer this becomes vital.