A motorcycle is not a car and why almost all motorcycle makers require 2 year brake fluid changes and more. Heck Yamaha calls for master cylinder and caliper rebuilds, brake line changes every 2 to 4 years.
A motorcycle holds 1/10th or less the brake fluid of a car and moisture will build up in the fluid 10 times faster. So a car will get maybe 20 years while a bike 2 years. 10 x 2 = 20
(above just an example of course)
Bottom line, I am sure everyone has heard of frozen calipers, broken master cylinders, ect. This is all due to moisture in the system.
Now, can Harley or any maker use metals that will not be as affected, yes, I am sure, certainly an issue in those model years but again, if the proper fluid maintenance was done as outlined in the manual, issue would not have happened. Not making excuses for the design, just facts. I would not be happy to have one of those bikes but I do not always change my brake fluid as required.