Because street bikes had not yet become so specialized in those days. Bikes had to do more than fit in a narrow niche.
As we entered the boom years of the late 80's and through the 90's people were willing to pay for specialized bikes that looked like they just came off the track, or were equipped like a 2-wheel Winnebago. But before that people wanted street bikes that were versitile and those that wanted a race bike or a tourer bought themselves a UJM like the CB, or the KZ, or GS and customized it to be a cafe, or track bike or a tourer. I also don't think that the manufacturers thought there was a market for a more focused bikes. They didn't want to get stuck with a bunch of expensive racing style bikes that couldn't be ridden more than 50 miles without back pain.