T.S, back then in Pride and in the beginning stages of MMA. It used to be more international. So it attracted anything from Savate guys, to full fledged K1 strikers and Muay Thai fighters.
When the UFC took over. Many kicking based fighters who were fighting in MMA, such as in Pride and Heroes, went back to their respective striking sports instead of pursuing mma any further.
Not only that, but this also put a huge stop of potential kickboxing type fighters that could have become potential MMA fighters.
Then we have the rulesets, and most detrimental, the scoring system which favor grapplers. Many a time we've seen fights where the striker actually hurts the grappler, but a simple non damaging takedown and lay and pray cements the round for the grappler. Not good for business to enter the sport when it's mostly stacked against you.
Then we come to the ring/cage issue. Almost all striking arts fight in a ring. A ring has corners and it is shorter. This allows the striker to easily trap their prey, leading to heavy damage that would score, or create the beginnings of a TKO or KO. In the cage however, being so big and having no real corner, the grappler is free to run away at will. And reingage when he is ready for a takedown.
This cage only favors guys like Stephen Thompson and Lyoto Machida as strikers, seeing as how they're very elusive and can use their footwork and the immense sizr of the cage to actually evade grapplers.
And even then, kicking and kicking defense has problem invaluable at the highest levels of mma.
Conor barely scraped a win over pretty much pure boxer Diaz by kicking Diaz legs out. Jon Jones barely scraped a win over pretty much pure boxer Gus by kicking his head repeatedly.
Anderson Silva was a great kicker who has used his kicks to win multiple fights and he wouldn't be the champ he is today if it was just his boxing.
When Fedor fought Mirko, he spent the majority of his training camp in Holland sparring K1 fighters and learning to kick Crocops legs out evertime Crocop went for a head kick. It doesn't make Fedor a kicker per say. But nonetheless he focused and learned the art of Dutch style muay thai for a while.
Plenty of Champions have been kickers, and this includes guys like Conor, Dos Anjos, Fedor, and Jones and many others who even though aren't traditional kickers, still use kicking to get that extra advantage to get wins.
And of course then we have the countless of traditional kickers who have made a splash in the sport like GSP (kyokushin) Mirko, Aldo, Lyoto, Stefan, Pettis (who looked near invincible at some point) Shogun, Mousasi, Overeem, Igor, Anderson, Thiago Alves, Brandon Vera, Chuck Liddell (Kenpo), Donald Cerrone, Uriah Hall, and the list goes on.
So. As you can see T.S. There's plenty of reasons why kickers don't even bother going into MMA. And the small amount that do always manage to be very successful and even become Champs. Food for thought chief