The biggest factor is as Seth put it "something better became easier to get". And right now "better than FX" is not that hard to get nor that much more $$, and keeps getting easier and more cost effective each year. Yup the FX looks good in the photo but this guy is 6'3". And even then the chest still comes down too far. Unless you have a good amount of height the amount of work to get FX to look passable (not right, we're talking passable) on a person can be more than simply getting more accurate (ANH sized) armor to begin with.
Would you let in a DP now? No, because why should you when FX is better and easy to get. We're moving to the point where better than FX is as easy to get. Unless of course, you're over 6'0"
On a somewhat related note I have some sympathy for black hole troopers. They are few and far between so it's not like there are a lot of troopers in "better" armor to be compared too, and the only kits that come in black ABS are FX. That said, I bet if a few dedicated souls started getting ANH sized suits & painting them, or at least upgrading buckets, there would be more pressure in that area.