I have very rarely been bored in PS, and only for very short periods of time.
Boredom is a state of mind found in each individual person. It can come from an unstimulated mind where the activity in question holds no interest, or a lazy mind which expects to be entertained. In either case, since it is a state of mind found in each individual person, it is the fault of that person that they are bored, not the activity. If the activity is not found to be stimulating enough, the person is at fault for either not changing their state of mind and view of the activity (yes, that is possible), or by continuing to do something that is boring them just as "something to do."
People with a lazy minds are unwilling to put any effort into entertaining themselves. They go into situations (in life or a game) hoping that someone else (be it people or game mechanics) will keep them from having to think for themselves. Though they say "What can I do?" what they really mean is "What can they have me do?"
So, no matter what your answer is to Mathy's question, the answer is up to each individual person. Everyone knows why they get bored. I am not going to ask you why you are bored. I am going to ask something else.
What are you going to do about it?
* Under the moon shuts the thread down and kicks everyone outside to think about it.
A creative mind can find something fascinating even in the mundane.