I think the problem specifically arose with Penman Ebony, and I was certainly one who suffered from this.
When I came back to the Netherlands in 1998, after 15 years of absence, I got myself my first fountain pen in about 25 years or so, a Parker Duofold Centennial, in classic black. I also got a bottle of Penman Ebony.
My pen did clog up fairly rapidly, as in, it started to refuse to write, which got worse and worse, until it stopped writing completely over a period of less than 6 months. At the time I didn't really know what was wrong, as I didn't know anything about fountain pens, and blamed the pen. You can imagine how disappointing this was.
In 2003 I received a Waterman Edson, and that was how I finally ended up here, and probably own about 80 fountain pens now ( I need to count them I think). I also found out, in that same year, that this was indeed a problem with the ink used, and that that was why Penman inks were discontinued, so did the people at the B&M store tell me (different place to where I bought the Centennial). Anyway, it was sent off to Parker eventually, and indeed, I got a new feed and even a new nib, after which the pen was functional again. I was shown the old nib and feed, and indeed, gunked up, to a degree where even the nib didn't get clean anymore without abrasives. After the fix, it did dry out rapidly, still, so I fixed that myself

.
BTW, the pen now leads a happy life, with yet another (italic) nib, in the hands of someone else, who absolutely loves it, after I made it into a cursive rather than a sharp italic, especially for him BTW..
Anyway, they also told me at the time that the problem was caused by the stuff that made it so nicely black, namely soot. Black ink generally contains ground soot to make it that colour, and since these are particles, they may block the ink channel if they get deposited in there. The combination of other stuff in the ink, and the rapid drying out of the pen (sometimes a matter of days), caused this phenomenon in my pen anyway.
I do think that the other inks in the range were taken out of production because they couldn't have a line of inks without black. Furthermore, certainly over here in mainland western Europe, most people do not use bottled ink, but cartridges only, which may helped the demise of these inks as well, especially as they were positioned as luxury inks, with a price tag to match.
I personally do like this ink (Penman Ebony) a lot, colour wise, but I do not care for its clogging properties, so it just sits there in a bottle, languishing together with a bottle of Penman Mocha ...
Warm regards, Wim