That pipe doesn't seem to do very well at producing much more power than stock in comparison to a real expansion chamber. It might, but the header tends to be so long it's probably before anyone could notice it.
If you don't know what exactly you're doing that pipe isn't so super useful and so it probably wasnt even popular enough to keep on hand..
The bulldog (not sure what they call it on other sites) seems to be far closer to the design that's needed, not to mention I've got experience riding that muffler, both the banana type AND the bulldog, and find that the older banana version didn't have quite the kick the bulldog does now, even with a leaking exhaust on the cylinder itself my friend's bike hauls some seriously strong ass. The only change is the pipe which was a bulldog welded to a header and that brought it to real serious life. Nothing like the old banana style that once was part of the same set up.
He is also using a jackshaft, which seems to work very well by keeping that nice powerband right in the gear ratios on the 8 speed cassette, maybe it's chance but it works very well.
So it would appear that the market is inclined to ignore the various banana pipes and looking to supply an actual bolt on power fixer-uper.
My 2 pennies on why they dumped the product.