I went from skiing 3 times to being a ski instructor. I went from snowboarding 1 time to being an instructor. In one instance it was a paid instructor and in the other it was not. Similarly, I taught people how to climb after just a few climbs myself. (I didn't start getting paid for it for several years after that but the "actual skills" I learned very early on. I wasn't as proficient at them without more practice but I could teach them.) As you said, that may be aptitude but I've seen a lot of people that took "a long time" to learn how to ski go on to be instructors in just a few months. The skills learned in skiing really only take a day or two to learn... perfecting them is what takes a while, just like in diving.
Again, being an instructor pilot, while not simple, isn't necessarily any more difficult than just flying. It takes more experience, but I don't know that it is any different than the 90 dives it takes to become a DM. (Can't remember how many hours you need before you can be an instructor pilot but I remember it not seeming to be a particularly high number.)
This could all be perspective, though. Either way, it seems that there is some element of marketing and some element of enthusiasm to show others how to dive or just dive more.
I just erased everything I wrote...ranted..about this post. After 2 years and 25 dives I am sure you are ready to teach scuba too.