Facebook probably has a lot to do with it. Death, retirement and career change probably contribute. Then there is the modus operandi of the employers. This started as a bonus thread, but I haven't seen anything about bonuses. I guess quango is right, or maybe you just have to go to each vendor and ask directly. Pay, per diem, and bonuses - call for details. If you can't muster the energy for a phone call, I guess it's not that important to you.