Three types of "BBW" come to mind.
a) "Genetically Big & Healthy":
Large frame with plenty of cushion for the pushing but still maintains a Healthy appearance, good muscle tone and a very womanly figure. The female body on a much grander scale. I have dated a few and the sex and BJ's were top notch. Not my personal preference in frame but I certainly see how this is very sexy to a great many.
These sexy BBW's know this about themselves and generally charge as much as any slimmer provider because they can get it.
b) "Lazy Big":
Small to medium frame but due to poor eating habits, health issues or lack of exercise maintains an Unhealthy appearance (Obesity). Typically poor muscle tone lacking in any real womanly shape aside from large breasts which are merely a byproduct of excessive fat.
They know this about themselves and generally charge less than most slimmer providers because they can get it.
c) "Genetically Big & Lazy":
Predictably a large frame with category (B) traits except on a much larger scale resulting in being extremely huge and obese in appearance.
They know this about themselves and generally charge Far less than most slimmer providers because they can get it.
Those providers who fit into category (a) usually have no problem showcasing full body shots because the total picture is still extremely appealing to a great many men.
Those who fit into categories (b) & (c) BBW's typically only provide tits, lips, eyes shots because they want to give the illusion you might be getting a category (a) BBW.
This however misleads many a monger who thinks he's getting a category (a) BBW.
There is a definite but much smaller niche for the (b) and (c) providers but I'm guessing most (b&c) providers don't want to be limited to a much smaller niche.
On occasion you will get a category (b) or (c) provider who for whatever reason perceives herself to be a category (a) and puts it all out there for the world to see while trying to pull off charging the category (a) rates.
These types of "Why isn't the phone ringing", "How does a girl get attention around here" and perceived "BBW attack" threads are the result.
This is just my opinion of course.