Interesting question, and one we have debated earlier as well. Why do classes rise and fall?

For the 18HT, I dont think the boats was to extreme, but they was expensive and early got a reputation for being fragile. I dont know if they really was.
The boats was/is tuned for upwind/downwind racing, a jib is nice to have when you want to go reaching (as you sometimes do when distance racing). Then there was the Worrel disaster..
The F-18HT also bore the burden of being directly compared with the F-18's. A 18 footer for two up sailing and nothing 'extra' to offer except higher performance and easier handling on the hard.
In addition, the boats was imported to the US. With a builder present in the US to supply boats and handle marketing, the 18HT status might be different today.

Generally, to build a class you need somebody like Wouter! Somebody who cares for the class and is willing to spend time and effort on building it. Without Wouter and Phill (and significant others. I haven't followed the F16's that long), I dont think the F16's would be where they are today. The F16's also have an extra selling point, you can race in the class both one up and two up on first to the finish wins. That is a really great point! But it's even more important to have someone to create activity, share information, gather everybody for racing (bring forth the whip) and create a group feeling. Without somebody to do this, it all falls apart until somebody steps forward and do the job.
Now, with a manufacturer in the US, it looks like the F16's are poised to really take off and reach critical mass.


Just my view on it, from the outside..