Out of curiosity, what's with the general dislike for JCM?

Corresponding JCMs have to be put into conforming clothing, whilst the weightmapping simply goes in with the rig. JCMs have their uses, as weightmapping (at least Poser's weightmapping) only moves vertices in a direction normal to the surface, a restriction JCMs do not have.....

Note that corresponding weightmaping also has to be in the clothing. 

Indeed, but that is transferred when the figure's rig is added to the cloth, at least in Poser...

But that is only a starting point, unless you are building skin tight body suits or get lucky. DAZ Studio does the same thing with weightmaps and includes templates for things other than skin tight bodysuits, which is still just a starting point. DS will (with Genesis and later) also automatically project the jcm's and other morphs onto the clothing, if they are not in the clothing. Again, it makes for a starting point but it certainly is not a one button solution. And herein lies the problem with new figures. To support them takes work. With good clothing it takes significant work.  For a content creator it is a financial risk.

Content creators have choices. Do they support an unproven character from an unproven entity, an unproven character from a company that has proven it fails at marketing their characters and support fro those characters, an unproven character from a company that has a proven track record which produces characters that sell content, or support an old proven figure where sales are falling off due to market saturation or customers moving on to the newer figures.