Snowbum has a reasonable discussion from his viewpoint on the oil cooler and why it was used on some models:
https://bmwmotorcycletech.info/coolers.htm
Sounds like the issue is that with the higher engine sizes and especially the use of fairings, the temperature goes up inside the engine. And it looks like it's not necessarily around town riding...unless the ambient temperature is quite hot...but rather high speed running as the heat output by the engine goes up in a non-linear fashion. He indicates that even a modest reduction in oil temperature can have a good effect on the oil used in the engine.
https://bmwmotorcycletech.info/coolers.htm
Sounds like the issue is that with the higher engine sizes and especially the use of fairings, the temperature goes up inside the engine. And it looks like it's not necessarily around town riding...unless the ambient temperature is quite hot...but rather high speed running as the heat output by the engine goes up in a non-linear fashion. He indicates that even a modest reduction in oil temperature can have a good effect on the oil used in the engine.