Why didn't main characters continue to move in War In Middle Earth?
It's a bug, this game was know for having many, MANY bugs. Although most of them were graphical glitches, I have heard of people speak about bugs that completely broke their game and they had to start over.
Otherwise, although you have played the game for a long time and I would assume you know it very well, you should read the manual. It is actually very useful and descriptive. If you find you are doing everything correctly and your characters/forces circumstances should allow them to move you can then be sure it's a bug.
The manual in PDF form. http://apple2online.com/web_documents/war_in_middle_earth.pdf