why SHAPE and SACEUR did not change their titles when Allied Command Operations was created in 2004?
The change from Allied Command Europe to Allied Command Operations actually represented an expansion of the mission and geographic area of responsibility for SHAPE rather than a complete change in the way it did business. In addition, the titles of SHAPE and SACEUR had great historical significance due to their continued existence since the beginnings of the NATO integrated military command structure.
Thus while some consideration was initially given to changing the name of SACEUR to something like SACOPS or even SACO, in which case SHAPE would have been changed to perhaps SHACO or SHACOPS, none of these acronyms were considered very dignified (somehow many terms ending in "o" have negative connotations, for example "psycho" or "sicko" or "wacko", and "SHACOPS" sounded like "shack ups"), and the two terms had never been formed simply on the basis of the command's name (thus Allied Command Europe's commander and headquarters had never been called SACE and SHACE ).
In addition there were important legal and fiscal considerations attached to retaining the name SHAPE, due to the many agreements and contracts signed by SHAPE over the years, so the decision was taken to retain the historic titles of SACEUR and SHAPE under the new command structure.
In the case of Allied Command Atlantic and its commander SACLANT, however, the new mission for this command was so completely different - overseeing the transformation of NATO's forces and procedures in the 21st century rather than guarding the sea lines of communication to Europe – that both names had to be changed, with the command becoming Allied Command Transformation (ACT) and its commander the Supreme Allied Commander Transformation (SACT).