Quote: There is the FA 600mm f4
Sure, it's even more expensive than the Canon/Nikon glass at that length and it's only on special order.
I think the reason why is pretty obvious. How many Pentax shooters do you think there are who want and can afford a 600/4? Even at the price of the EOS version.
Really, who could really afford a Pentax 400/2.8, 500/4, 600/4, 800/5.6?
And if you could, priced higher than the Canon versions (and certainly the Nikon) because of the insanely low volumes, you'd soon realise that you could get a Canon body and long tele lens kit for less than you could just to get the Pentax lens...and not a mug's body either, a nice 7D or even 5D body...
...I would be amazed to ever see a long fast tele prime from Pentax (but maybe there is a small chance of a 400/4, like it or loathe it) ever again. Maybe if market share got up into decent double figures again...maybe...
PS - I'm not counting MF lenses, you might see 600m MF lenses again...