When I add from another Excel (2003) file into one of mine, I unfortunately
also inherit all of their styles. I have a file currently with about 50
styles from other people of which about ten of those are different "Normal"
styles alone.

I know how to delete them one-by-one via Format, Style, Delete (what a
tedious process, MS!) till only those remain that I prefer.

Is here a way that I can select at once all those I don't want and delete in
a single stroke?

If not, can someone explain why MS did not allow for this?