The fact that they lasted this long, have a standard of perfection, and had some purpose that was different from other breeds tells me that they are more important than some backyard breeders try at making a breed with few numbers and little experience. Those birds will be forgotten quickly and the new breeder will lose interest when it doesn't turn out like they thought. But you are right about them dying off without interest in them today. Most just want the latest fad chicken
They made it into the standard because they were significant at the time, and had numbers. If they still had purpose why would their numbers be so low?
The current assortment in the standard represents only a fraction of the potential phenotypical diversity that is possible. Chickens have an enormous wealth of mutations, many of which have never been incorporated into breeds and varieties. How many large fowl breeds are in the standard that have a single comb, and, if you had to describe them to a non-fancier, would sound exactly the same?
I agree that most peoples' efforts to make a new breed won't be successful. Even if the competence, finances, and vision are in place, the need for consistency over multiple decades will end most projects. However, I do think it's important that people be encouraged to pursue their passion. Everyone begins with inexperience. I took on a project at 15 years old and failed because of incompetence. I learned a lot from that project and my failures and am now trying again.
Also, isn't this all for fun? If someone enjoys keeping the old breeds alive they should do it. If someone enjoys crossing different breeds together to get something new, why not the same? Any breeder, whether of old or new, regardless of how long they last, should enjoy what they are doing. If they have that what more could you ask? Like anything in life, it's more about the journey than the destination. If the destination is reached, great, if not, enjoy the ride for however long it lasts.