You are thinking purely in a MUSICAL sense .
The reason is this... many of the variations in merengue, can be readily transposed to 4 count, and even some latin hustle .
Most dances " borrow " from each other . The Rhythm dances are notorious for this... altho, some of the ballroom dances are equally adept at doing same .
The " purity " of virtually ALL dances , has long disappeared ( Locksteps in T/Arg )
V.W. and Sq. Rumba are possibly the only ones to have retained more of their intial concepts, by and large .( but...the Amer. style VW has been embellished beyond belief )