Later I learned that cathedrals were always oriented with the altar at the east end. Why is that? Is that where we get the word "oriented"?

Many old maps (say 13th C) were made with the East at the top, not North. The word 'orient' is from the Latin, oriens, which means to rise. I hazard a guess that it was easier to align maps with where the sun rose than with north when you didn't have a compass.

I can't really say about church buildings!