Non-precision approaches for which constant descents are not approved?
Probably because it's so shallow: you have 8+ NM to descend about 1100'. On a 3 degree angle, you'd typically decsend 1100' in a little over 3 miles.  I'll leave it to good folks with calculators to work out exactly what angle this would be, but it's under 1.5 degrees, so probably below whatever limit TERPS gives for depicting an angle there.

One solution would be to remain at the FAF altitude until reaching a calculated "fly-off" point, at which time you would descend at a 3 degree angle until reaching published MDA + 50', at which point you continue or go around.  But that probably takes specific FMC software &amp; perhaps a tailored approach chart, so with only this one your option pretty much looks to be "dive" (not that far) "and drive" (quite a bit).

Though that gets you to an MDA that is 1700'+ above the TDZE...

ACTUALLY, ON FURTHER CONSIDERATION: It isn't too shallow, it's a steep path from FAF to TDZE, 3000' in 8 NM (would be 9NM at 3 degrees). And the angle to do that probably doesn't quite clear the WAGOK step-down, meaning your vertical path becomes even steeper at that point than it starts out.

So rather than publish gradient***s*** steeper than (whatever the TERPS limit is), and increasing after the step-down fix, they just say NA &amp; let you "make it work" on your own. 

I notice that there is no VDP published here, either...