Because your foot would go right through the computer screen!
Spine
an Envelope EDIT: My deepest Canadian apologies to those who are calling this a riddle. I always took it as a cheesy joke
Empty Magazines.
By e-i-e-i-o-mail.
Because then it would be a foot
A yardstick.
To stamp out forest fires !
I don't have a stamp collection.
Because otherwise they would be unable to track movement and move the cursor in the computer screen.
He wanted to check his e-mail.