Why do almost all laptops not come with a built-in handle? That is the quintessence of a portable item. Forget the bag.
I think the Toshiba Toughbook had a handle. I think many folks here, given their druthers, would design something that looked like a Toughbook, then become disenchanted with it for various completely foreseeable reasons, and go back to using their standard issue MBP.
(There were generations of these with handles, but at least in the early ones, the handle didn't dominate the dimensions - things like "removable drives encased in impact gel" did.)
(And if you go much farther back, the TRS-80 Model 4p - but "sewing machine class" portables kind of had to.)