Over at PLOS ONE, Stefano Ghirlanda, Alberto Acerbi, Harold Herzog, and James A. Serpell have looked at the rise and fall of Kennel Club breed registrations through the matrix of breed health, longevity, and such behavioral qualities such as aggressiveness, trainability, and fearfulness and what they found was that breed popularity is based solely on fashion rather than any inherent desire or attribute of the dog.
The popularity of dog breeds shows, over time, the kind of large and apparently whimsical fluctuations that are usually considered the hallmark of fashions and fads. Registrations of Irish setter puppies with the American Kennel Club, for example, climbed from about 2,500 in 1961 to over 60,000 in 1974, only to drop to about 3,000 by 1986. Many other breeds exhibit similar fluctuations. ... We find no indication that behavior, health, or longevity have been important in determining breed popularity. The data show, rather, that the most popular breeds have significant health problems, and possibly more behavioral problems. We conclude by discussing the significance of these results for animal welfare and a broader understanding of cultural dynamics.
The authors go on to note that:
We find a strong positive correlation between a breed's popularity in the U.S. and the number of inherited disorders from which the breed suffers, and no correlation between number of disorders and breed volatility or rates of increase and decrease around popularity peaks. We also find that breeds with more disorders have decreased in popularity in 1996–2005, a result that parallels a similar, albeit weaker trend observed in U.K. data. Altogether, these findings suggest that popular breeds carry a significant health burden, and that in recent years the public may have started to avoid breeds with more health problems. The latter effect is statistically significant, but not large: number of inherited disorders explains only about 10% of the variance in popularity changes in both the U.S. and the U.K.