What is the rationale behind timeouts?

I logged in to my course account yesterday, left it open, and today I found the login screen sitting where my studio course’s syllabus should have been.

Why is a timeout even necessary? To force students to take breaks? These annoying timeouts are there even if you saved the pages onto your hard disk.

Why is this happening in this program in particular? Isn’t our program the unlikeliest place on earth that this happened? I am sure this is an act of exclusion at least for blind people, people with learning difficulties, or people with motor impairments. Did the programmer even try out that green dot computer interface thing? Are they telling us to block the timeout code as if it were a virus?

Why are all web sites getting less and less usable? What is it, really, that we—the design, IT, and engineering professions on the whole—are striving towards? Isn’t our goal usability and not uselessness?