Hot/dusty operating conditions are easy to understand. But short trips, especially in cold weather, are at least as problematic.
When you cold-start a gasoline engine, there are two problems:
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The piston, piston rings, and cylinder bore all have a sloppy fit because they’re not up to temperature.
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The computer is injecting extra fuel to ensure the production of a combustible fuel-air mixture under cold conditions. Not all of this fuel evaporates.
During a cold start (and for some time after), some of the fuel entering the combustion chamber as liquid, sluicing down the walls of the cylinder and getting down past the ill-fitting cold piston rings, along with plenty of gaseous combustion products. All this stuff ends up in the crankcase, where the oil has to deal with it. There are emulsifiers in the oil to assure that the water stays mixed/dispersed instead of stratifying in the crankcase, and there are other additives to deal with the gasoline and combustion products that end up in the oil - but they can only do so much. If you go for a good long drive, especially at highway speeds, you heat the engine up to its normal operating temperature and keep it there long enough to evaporate the water and gasoline out of the crankcase oil. If you barely get the engine up to temp before shutting it down, then all that junk stays in the oil, until you add even more of that during the next cold-start.