Perhaps the low mileage tells the story. They haven't been ridden much. Not unusual at all for motorcycles to not be ridden much and then the owner sells rather than keep paying insurance and suffering depreciation or making payments in one of those situations. One owner did say he was in the military and was being transferred as his reason. When I bought my 85 Kawasaki in 2009, it had 1k miles on it. When I bought my 89 Venture in 2014, it had 6k miles on it.
The drawback to buying a BMW in my opinion is that they are expensive, parts and labor are very expensive and overall I don't think they are as reliable as a Japanese bike. The good part is that the engineering is top notch. I've never test driven a BMW auto because I've been afraid I would buy it! LOL!