What you're forgetting is:

1. People have to read this calendar. 2. People have to edit this calendar. 3. Other people in the office don't know Excel as well as him. 4. Other stuff is designed to work with our calendar software, but not excel.

A hammer can drive a nail into wood. With a little help, it can also remove nails, smash glass, and pry things open. But if you're using a hammer to stretch pizza dough, get help.