Why we never see any problems based on calendrical calculations in sport programming ?

In my 1 year of solving problems on codechef and spoj i have never hit upon a single problem that deals with Calendrical Calculations .

Why do problem setters avoid creating problems dealing with calendar calculation ?

You can’t make any problem which makes some sense for competitive programming, using only calendrical calculation as main part of it - it will be simply “do you know how to write a code which works” without any idea behind it.