IF...and i know its a really big "if"....but, if these things could be bought as a complete package....like the 440-1 kit, with quality parts in them, assembled by a reputable shop...for around $5000...they would probably sell okay.
people like being able to buy a "package" that has all the components in it, and all the normal BS that can go into trying to match parts from different brands of stuff together, already worked out.

while the ICH stuff is a little on the "rude and crude" side....if you buy one of their head packages....you can usually bolt it all together with a minimum of hassles.

not everyone who is putting a motor together has easy access to a machine shop...so the less reworking the parts need...the happier the customer is....and then word gets around.

while these are really nice heads....the fact that MP kinda leaves you hanging after youve bought them will probably hurt sales...well...that and the price.