The first two one designs EVER in small-boat sailing are both sailing happily today, and they were both created in 1884. The first International small-boat class is one of the most popular singlehanders afloat, and it was designed in 1912. The first International yacht class is still popular and still Olympic. The second one design cat class (Shearwater) has been around for over 50 years, I think. What is the most popular cat class? Hobie 16 - pretty much the same boat for 35+ years.
So the plain and simple FACT, however much you may dislike it, is that one designs classes DO survive, and some of them have survived much, much longer than many development classes. Seen many Cs, 18 squares, or Ds lately?
So, if we look at the classes you mention (I'm guessing one is the Star), we'll see that they are exactly as designed when they became a class? The Star has seen rig and sail plan updates through the years. They are no longer built with planking on frames. The Tornado has seen updates through the years. Just about every OD class that has had long legs to it has been able to update to keep somewhat current and relevant, either from a materials or design modification standpoint. Now that we've given some examples of long-timed OD classes, I'm sure we can come up with a larger number of one design classes that have also died over time. AMF Alcort brought out the Force Five as a one design alternative to the Laser. Don't think it's much of a class these days. Hard to find big Hobie-14 OD action in the states (one of the biggest shames I believe) - and, yes there are small pockets around, but not really a strong OD scene. Seen a Prindle 19 regatta lately? The Point is - being one design does not automatically guarantee success. And not updating a design from time to time means that at some point it becomes "quaint" and will become less attractive. Even Optis have developments that have been applied through the years.
I think a big killer in OD is the single manufacturer supply concept. You can't race if you don't buy your tramp from the original builder. Same with sails. What crap. Prices go up, quality goes down. I've crewed on Flying Scots - old OD class that would support your premise. But you can buy sails and other parts from a variety of manufacturers (just must measure in). And while I'm not up on complete Flying Scot history, I'm sure there have been rig updates voted in through the years.
In keelboats, by far the most participation in racing is NOT in OD. It is in the legions of people that bring out whatever they have and race PHRF on Wednesday and Friday nights, all across the nation.
But all that aside - to build cat sailing, either in the racing venues or as a past time, we need to bring fresh blood in. New sailors will revitalize old and new classes. Restore the critical mass.
