Could you explain why the kettlebell does it, what is the cause to this effect? Why will bodyweight, dumbbell, barbell, etc not build it?
1) eccentric loading, and 2) the exercises that tend to make up a training session/program
Let's look at eccentric loading. "An eccentric contraction is the motion of an active muscle while it is lengthening under load. Eccentric training is repetitively doing eccentric muscle contractions," according to Wikipedia. Also in that article, "The energy that is absorbed by the muscle can be converted into elastic recoil energy, and can be recovered and reused by the body. This creates more efficiency because the body is able to use the energy for the next movement, decreasing the initial impact or shock of the movement. "
"What’s so special about an eccentric contraction? The eccentric contraction is the strongest type of contraction your body is capable of producing while actively moving. Studies indicate that as much as 20% more force can be generated during an eccentric contraction when compared to a concentric contraction. " That quote is from this article by Ian Padron on Dr. John Rusin's site.
In the kettlebell snatch, eccentric loading between reps is a huge part of the exercise. In the barbell snatch, which I've been practicing a lot lately, there is none of this. The exercise is all about getting the weighted bar from ground to overhead. From there, it is dropped, or at least lowered with minimal impact, not trying to create any elastic recoil energy to generate another snatch. In a dumbbell snatch it is mostly like a barbell snatch. I've done some dumbbell snatches that are fairly light like kettlebell snatches, but it gets awkward and grip-limiting pretty quickly. I don't think I could load a dumbbell snatch with eccentric loading nearly as heavily as a kettlebell snatch. Similar comparisons can be made for the clean, and to some extent even the press and squat, though less so. And of course the swing, as there is no barbell equivalent to the swing. You can swing a dumbbell, but again the grip and awkwardness restricts the loading of the movement a lot more that the kettlebell with the super-convenient handle.
As far as the types of exercises that tend to make up a training session, the eccentric loading and elastic recoil makes it possible to do more lifting overall. Much like an experienced runner is much more efficient at running because their tissues have built up this recoil ability, saving the need (like a running newbie) to get every bit of force production from muscle contraction, an experienced kettlebell practitioner can move the weight over and over, with a heavier and heavier load, making more and more use of this elastic recoil action. The tissues get really rugged and tough through this repetitive work. Thus the "old man strength" and "farmer strength" that people refer to.
Most of that pertains to "kettlebell ballistics" more than "grinds", but they also have an advantage, in my opinion. That is, freedom of movement. As you know I spent all of 2018 doing almost exclusively barbell strength training. When I get back to the kettlebell at the end of Feb 2019, it was like being let loose from a cage (or squat rack)... the freedom to move in so many planes of motion, so many different movements, such variety was very refreshing. Did anything restrict me from this while barbell training? No, but I didn't load the movement, because my training with load was squat/press/bench press/deadlift and a few varieties of these. The variety of loaded movement in get-ups, bent presses, bottom-up presses, carries, etc. in addition to the ballistics was all really great to get back to. So... the kettlebell is here to stay, for me, even when it doesn't make up the primary aspect of my training (which is currently the case again, as I'm doing a weightlifting program; C&J and snatch with the barbell).
On a final note on grinds, specifically presses, much is made of the off-center nature of the weight in overhead presses. I don't know enough about shoulder mechanics or musculature to comment on that, but it does seem that a lot of trainees can do more volume of pressing with kettlebells with less problems, and get lots of benefits from it in strength, hypertrophy, muscle definition. That said, I think overhead pressing a barbell is pretty awesome too... And getting even more weight overhead with a barbell jerk... well, that just might be the king of exercises. But that's just where I'm at here lately.