People don't get in front of their computer right away when the tournament starts. I notice in a lot of the tournaments I play, the first hand is extreemly slow, untill the people that arn't there get auto sat out. Also it is really slow after break for the same reason.
Somtimes when I'm in a big hand and playing multiple tables I will be focused on that hand and miss my turn at another table. I try not to do that because I don't want to slow down the game... However, it happens and I'm sure I'm not the only one.