Short trips will leave water (condensation) in the oil. Warming the engine up will "liberate" the water (basically boil it off) and can show up as "milky crud" in the filler cap. Finding "milky crud" on the dipstick is worse.
Longer runs will boil it all off, thus better oil and less/no "milky crud". Some call it "brown mayonnaise".
Short trips is part of why ALL Mfrs consider this "severe duty/service" and call for shorter oil change intervals.