IIRC, the reasoning is mostly about failures of parts/screws involved in the maintenance.
The labor required to tap a seized lug or corroded filter that gets stuck is a multiple of the cost of oil change. There may be temperature related reasons as well, but getting facts about a topic that fuels passions as much as motor oil is difficult.
With some egregious appealing to authority.. I will say that as someone who performs oil changes on our daily driver Honda Element, a 1987 VW camper (when it both had the original engine and the new ford Zetec engine it currently runs on) as well as my 2001 BMW motorcycle, 1970s cub cadet lawn tractor and the Harbor Freight engine I transplanted on to the snowblower...
I have never once encountered a ceased sump plug or stuck oil filter. Ever.
I'm not saying the monkey at Zippy-lubers wont strip a plug because he was busy texting his girlfriend at the same time. But I've pulled parts of engines that hadn't see action for decades. This is not a reason for a 6 month schedule
The only advice I've seen, and oddly enough it's not been mentioned in this thread so tack it onto the list of oil change folklore, is acidic buildup due to oxidization and the timeframe on that is roughly a year.
IMHO 6 months is much too short of a minimum interval for modern oil. 12 months is a much more reasonable interval.