OK, Lets have a bit of perspective here! Bikes corroding is nothing new, even the same model and model years can sometimes vary enormously in their battle against corrosion.
Whilst I agree that some time and care needs to be given to preserve our bikes as much as possible, we should not need to be anal about cleaning for the bike to last a fair few years before showing any significant signs of corrosion.
In my 45 year biking history I've owned over 100 bikes, many being new or nearly new. I ride all year and I've looked after them all in a similar manner.
Here's my system. Summer...Wash off the bugs occasionally. If it's been a wet day and the bike is blathered, wash off at the next opportunity. Winter...If the roads are wet and the bike is blathered to the eyeballs, round to the nearest Jet Wash, wash it down come home, quick rinse with the hose wipe down put it away.
Twice a year...Spring (April) Autumn (September) thorough clean and a good polish. Usually takes me most of the day.
Here's some of the more memorable bikes in relation to corrosion, all looked after in a similar manner to the above.
1976 Suzuki GT 550...looked like a 10 year old bike after it's first winter.
1985 BMW R65....2 winters still looked like a brand new bike.
1983 BMW R80RT.....Significant corrosion after 2 winters
1987 BMW K75... Kept this bike for around 8 years used it to commute, no corrosion at all.
1988 BMW R100rs... Fair amount of corrosion after winters, but still looked good.
1992 BMW K75... Still see this bike now and it's still in great condition and never been renovated.
1994 Triumph Sprint...Almost melted before my eyes, never had anything corrode like this did.
1996 Triumph Daytona...They did me a deal on the Sprint. This was better but still significant corrosion after one winter. Put me off Triumphs for a long time.
1997...BMW r1100gs..4 Winters looked almost as good as new.
2005 BMW R1150 GS SE...Not the first owner, but at 4 years old did not look it's best significant corrosion all over the bike.
2009 BMW R1200 gs... 2 winters almost unmarked.
2011 BMW R1200gs tc..2 winters...as new.
2013 BMW R1200 gs wc.... Not quite as bad as the Triumph sprint. but not far off. 16mnts old looked like a 10 year old bike. Biggest loss I've ever taken on a bike.
2014 Moto Guzzi Stelvio...17 mnts indistinguishable from new.
2015 Triumph Explorer....Long time since I've seen a finish as good as this, and in no way was it pampered.
So, there you have it. Fair few BM's in there some were finished really well and some not so. Best finish I've ever seen on a bike were the K75's. I've had 4 two of which were fairly well abused, but stood up to it very well.
I've used garage Jet Washes on most of most of my bikes and have no evidence to suggest they promote corrosion. I see were your coming from with the caustic pre wash. But your washing it straight off.
If modern BMW's won't tolerate this without corroding...time to move on.