My guess is they're looking for patterns...all part of the total package. ie does pilot call in sick consistently over holidays/weekends/etc. If a pilot has dependability issues, then yeah, the airline probably is going to have some pause hiring that person whether that's fair or unfair.

Having a medical issue where a chunk of sick time is used is not going to work against a pilot. But having issues that keep popping up over holidays may call for some 'splaining. My .02