The manufacturer recommendations are controlled by the marketing department. Here’s a cut and paste about Subaru oil changes…
Severe driving is
Repeated short trips, stop-and-go, extensive idling (basically any urban driving)
Rough, muddy, dusty, wet, humid, cold, mountainous, salty conditions (basically any country or winter driving)
Towing a trailer.
*NOTES
#1: under Severe driving replace ever 3,750 miles. Turbos must have the synthetic oil service done at least every 3,750 miles or 3 3/4 months
More than a few engines develop oil consumption issues at an early age due to not adhering to the above and quite a few of those engines had an early death due to oil sludging, oil coking, or running the engine too low or out of engine oil.