I am not sure it is fair to say there is much of a gap between the scientific literature and the DSM. The DSM is a consensus of experts and it was just updated in 2013.
I think the question you are asking is why doesn't the DSM align with all the amateur self-help books and Internet blogs?
There are two reasons I can think of.
Most amateur self-help books and Internet blogs don't understand what personality disorders are and lump every ex relationship partner "from a relationship that ended badly" into the mix. This inflates the population by a factor of 300 - 400%
Less than 12% of the population has a clinically defined personality disorder. However, if you add the incidence of all 10 disorders, you get a much higher number. Why? The category of personality disorders greatly overlap. Adding them is double, triple counting and this greatly inflates the population numbers.
Currently 29% of the population qualifies for either an addiction and/or a DSM mental illness label. This is a staggering number and many clinical experts believe it is already too high. I don't think there is much consensus to make the number higher.
Nina Brown PhD said it best. Most of us are dealing with personality traits of these diseases (not the disease) and that is enough to cause the problems we experience. Learning the tools and coping mechisms for dealing with these disorders apply. And that is why we are here.
I'm personally a fan of the idea of mapping every trait on a scale of 1-10 in a 3d model which shows which areas are affected. Then separate the areas into different PDs/ fields i.e. emotional, antisocial etc. That way you can say they have an emotional disorder with strong antisocial traits.
Not too practical in an inner city emergency room... .the data gathering alone would be prohibitive... .
There has been a much simpler mechanism in place for years - a person must first qualify as having a Personalty Disorder (generic) before it is sub-categorized. Most people miss hurdle/gatekeeper and jump to the trait lists like reading a cookbook.