You are so right! Why the bulb is so gratifying is something of a mystery to me, too. I suppose for those who were given enemas early in life, and had the seeds of their fetish planted then, that might be the answer. Childhood enemas, from what I gather, were often (usually?) given with a bulb, so an OTK bulb enema takes the receiver back to the root of his/her fetish. In my case, I was 30ish before I was given my first -- certainly the first I can remember. Enemas were not used in my childhood home, which was in the '50s, still well within the time of frequent home enema use among the general population. I've covered this in detail in other posts, so I'll just say, my introduction to enemas was at the hands of my ex-wife, and her use of them was strictly for erotic pleasure -- no pretense of being for health or hygiene whatever. She'd alternate between the bag and bulb, seemingly letting whim make the decision as to which. When I'd be given multiple enemas, she'd sometimes use both.
For those who haven't been treated to both, it might seem that an enema's an enema, regardless of the equipment used to give it. I can say that for me, at least, that's not true. The overall experience is similar, of course, but different enough to make the distinction when talking about it. The bulb seemed more intimate. I don't know exactly why, but I suspect it started with the simple fact that my giver used her own strength to force the injection, not gravity, and in my ex-wife's case, used the thumb and middle finger of her free hand to spread my crack and expose my anus for insertion. A more tactile experience for both partners. She used an 8-ounce "adult rectal syringe", but did not go to extra effort to empty the bulb into me each time. She'd probably get something like 5 or 6 ounces in, then withdraw for another refill. This meant more insertions and injections to the bowlful of 2-1/2 to 3 quarts warm Ivory solution. That extended both the length of time and number of times I was receiving the magic.
A bag enema, after the clamp is released, is a pretty silent affair -- all of the intense sensations are in the bowel, with whatever external sensations are provide by the hands of the given (massage) . With the bulb, the way my ex-wife worked it, there was wonderful "audio" to in addition to everything else. She made a deliciously noisy affair of refilling -- she'd squirt the remaining solution into the bowl after each withdrawal, which agitated the remainder enough to keep it mixed and at uniform temperature. Then, she'd squeeze the bulb with the nozzle immersed, which made a distinctive sound and sent a clear signal that the process was still under way and under her complete control. I still loved the bag enemas I got back then (and after!), but the bulb was something special. It kept her authority over me at the forefront, widened the gap between her, the Dom, and me, the Sub. The bulb was not as convenient to use as the bag, but the extra sensations it brought to the moment made the extra effort worth it!