[M T]

Why is "Computer Science" not called "Computer Engineering"?

Depends upon your definition of science.  If you define science as studying strictly the "natural world", obviously that doesn't apply to the part of CS that studies algorithms and such.  In some sense, it is more like mathematics, in that CS deals with theories of how man-made systems (similar to sets of axioms) work.  But, like science, not everything is purely proofs of theories; some areas deal with theories and accompanying experimentation to test those theories.  Certainly when you get into more complex systems (think of the Internet as a system), there will be features of that system that are beyond being provable (I offer that opinion without proof). 

Like the scientists at SLAC, most computer scientists have to be pretty adept at what one might call computer engineering to build systems in which to test their ideas.  Some of the most prominent computer scientists are strictly theoreticians and don't build systems at all themselves.

[M T]

Why is "Computer Science" not called "Computer Engineering"?

Depends upon your definition of science.  If you define science as studying strictly the "natural world", obviously that doesn't apply to the part of CS that studies algorithms and such.  In some sense, it is more like mathematics, in that CS deals with theories of how man-made systems (similar to sets of axioms) work.  But, like science, not everything is purely proofs of theories; some areas deal with theories and accompanying experimentation to test those theories.  Certainly when you get into more complex systems (think of the Internet as a system), there will be features of that system that are beyond being provable (I offer that opinion without proof). 

Like the scientists at SLAC, most computer scientists have to be pretty adept at what one might call computer engineering to build systems in which to test their ideas.  Some of the most prominent computer scientists are strictly theoreticians and don't build systems at all themselves.