Because I have visual studio open, a solution loaded and organized with all the files I need for this sprint, SSMS with the servers all connected that I need, all my tabs open to see my jira board, support tickets, etc, a notepad doc i was using to take notes on a phone call, my ssh key loaded into pageant, and if my computer reboots, i'm going to forget half of that when it starts back up and lose 30+ minutes trying to get set up again the next day.

edit: i would legitimately quit a company that made me reboot every single night.