Because it's too big, and the lack of a proper 'sleep' mode is beyond vexing. I like having a document open, be working on it, being able to turn off the machine and then being able to come back to where I was without going through a boot, opening the document, etc.
It's a small annoyance, but given it doesn't do what I want it to do (take notes easily and rapidly) then I'll go back to the Sig3.