I don't know why CIM would be appealing to a female, but I am glad that some allow it.
For a male, I have a "scientific" explanation of its appeal. First, consider that the head of the "joystick" has many more pleasure sensors (millions of 'em!) compared to the shaft of the joystick. When the joystick is stroking back and forth inside the "normal" - uh - "socket" (CFS), the circumference of the shaft gets almost all of the attention, the head not so much. During a BBBJ, however, the head and tip are getting plenty of stimulation from the female's tongue, cheek, palate, and throat. This is one reason most men want a BBBJ and not just straight CFS, and also why it is the quickest way to "prep" a guy for CFS. Now, during the BBBJ when you remove the joystick prior to the moment of release, for COB, COT, COF, you are depriving those attention-hungry sensors in the head, whereas if you leave the head in there at the climactic moment, the head sensors continue to receive exquisite stimulation which then
adds to the pleasure of the much anticipated "release of joy" from the joystick.
Aside from the purely physical, there is also the idea that a CIM is the ultimate "acceptance". A woman is taking your DNA, that which makes you YOU, into herself like a dearly desired dessert. It is nice to know that some women actually think of it as such.
Of course there is also the visual of such a submissive act by the female. That's just plain HOT...