I see you're having an oil service life discussion in the dark. Let me shed some light.
This is what $35 gets you at Blackstone. There are other labs...
$25 won't include TBN, which is the really important for judging oil age. It's a measure of the pH buffer remaining. A "buffered" solution has additives that will neutralize both acid and base addition, to maintain pH in the target range. An oil with low TBN has a worn-out buffer and pH will start to drop soon.
Looks like I had some life left at 25K (nearing 35K now).
To Snow's point, the engine is designed to run at high load, for efficiency. To wb8's comment, it's only running half the time, but that means lots of cold starts, operating below operating temperature, and in Winter, never achieving operating temperature.
I would expect both aspects to hurt oil life by virtue of increased blow-by on the power stroke. Crankcase ventilation removes most of those gasses, but some still dissolve in the oil and eat away at the buffer solution measured by TBN.
I've got full synth 0W20 in now, so we'll see how the fourth change differs.