The reason to "Why" they are not there, could be:
Mutants with three straps are almost useless in waves (because of the three strap itself), and the flat rocker and straight tail/edges make them even more useless in waves...
Okay, so they are definitely not waveboards, okay.
Then we could use them for freestyle ?
Hmmm, no, they dont actually land well backwards from super powered megaloops
Besides, no advantage in freestyle, to have to jibe
So they are not good for freestyle either (not bad, but compared to a TT they are...)
What about light wind then, because of the flat rocker ?
They are not bad for lightwind, but compared to even the smallest freeraceboard, they suck, because they are waaaaay too narrow.
Even a skimboard with or without straps are better in light wind.
So instead of having a board that is equally well at all three (waves/freestyle/light wind), you have a board that is equally BAD at all three
I am pretty sure this is why they dont really exist no more...
There is ONE thing they do better than everything else though - JUMPING HIGH !
They can go fast as hell, lots of control in chop, and good grip with the rear fins - so awesome jumping machines
BUT, in 2004-5-6 we loved boosting as high as possible, yes.
Today, it gets really boring just boosting, and we want more and different things - namely riding waves, OR technical freestyle, OR light wind.
And all three disciplines, also for the freerider, are three very different boards
We are so "spoiled" by having so many good boards and riding so many years, that we dont want boards that are to much of a compromise, and dont really do anything really well.
Riding back and fourth and jumping high is only fun the first years - then it gets boring and we want to explore all dimensions of kitesurfing, and not just this very "basic" state of ones progression
At least this is why I think these "older" mutant boards are extinct today
Then 5-6 years ago, the wide two strapped mutants were "almost" popular a year or two - they worked better because they were wider, and could be used in waves for rookies who could not jibe.
Again - they all turned out to be too much of a (bad) compromise for the public, so only a very small niche nowadays (and around here noone is riding these today actually)
But a three strap wide light wind mutant ? Why ?
You got the wide Shinn and the Norht Skimfish etc which are better IMO, and two strap.
My point is, those old classic mutants sucked in waves, and not good for freestyle nor light wind either - so "worked so well in these conditions" you say ?
Nope - only according to the "time back then".
Go ride one today, and compare (we have done that, just for fun - and discovered WHY they died).