Well in my case I can blame too many cooks in the kitchen as I work in a big corporation and each department only thinks of itself. More directly in my department, it's similar as all the artist used to be on one team and reporting to one manager, but they restructured and now we're split between four teams and four managers yet still do each others work as needed. Thus if one team lets their artists take vacations at the same time, the other teams get to pick up the slack. Only problem is the other team shave their own projects.