Which gets back to why it never gets practiced. I use them becuase I they tend to be a natural follow to a lot of upper body techs for me. If you don't know and it and it is not natural for you, you won't practice/learn it and there for won't use it.
(
IMO)
It has less to do with being 'natural', or a follow up attack that flows with certain combos (ie: jab, cross, step, spin hook [similar to above gif]), it has more to do with the risk outweighing the reward. I could throw that kick all day if I wanted, but I won't. If I'm going to throw a spinning kick, I'm aiming for the head or body, not the legs.
No matter how much you practice spinning kicks, there will always be a point where you're ''blind'' and your back is turned to your opponent. Adding a little more power to a
leg kick will never make attempting that attack ''worth it'', even if you're comfortable with throwing it. The only time I could see it being used 'comfortably' is if your opponent is timid and way outclassed, but that goes for most flashy, high-risk techniques as well.
More power to you if you can execute it
consistently, I just don't think it can be done at a high level in MMA.
[edit] I understand and agree with what you're saying though.
Spinning techniques in general aren't used as much because most fighters just haven't been trained to (or flat out can't) execute them properly. They aren't comfortable enough to land them, especially considering the risk involved. The fighters who do throw spinning kicks often usually come from a kicking background, and they practice those techniques regularly. It's not really 'branching off' for those guys, so it doesn't interfere with their 'MMA' training.
The question is how to get fighters/gyms with more traditional wrestling/boxing backgrounds to incorporate more 'intermediate' level kicking techniques that aren't used as often as the common leg/body kicks we see most fighters throw. As you mentioned, they are sacrificing training in an area they are comfortable with/good at to attempt to learn new techniques that won't necessarily be beneficial for them (for a while at least, if ever). Even if they do become adequate/good with them, they still spent a lot of time training techniques they will rarely use, and are still higher risk techniques than what they would have been practicing. It's all a gamble, which is why I feel so many trainers/fighters tend to use the more basic techniques. (I don't necessarily agree with that philosophy btw. I really enjoy the fighters who learn to incorporate more 'unorthodox' or rarely used TMA techniques in their MMA striking arsenal [Pettis, Le, etc]).
