If you plan on getting 20 cubers and only 6 show up who are coincidentaly good friends, it will just be a meeting with official results instead of a real competition in my opinion.
If you have a competition on a Wednesday night, don't advertise, had it announced only one month ahead, and you get only a few people, I would guess the board would reject it.
However, if you have a competition in a new area, advertised it months in advance, and 10 people showed up, 7 of them new cubers, and there was many no-shows because of a snowstorm, should the results be official?
a well organised competition will never have too few cubers to compete anyway in my opinion. A smart organiser checks about how many cubers will come and from where (ish).
It doesn't matter how much you check. Some people will say they'll go to a competition, but then for whatever reasons, don't show.
The only reason I can imagine of getting too few cubers is when after you announced the competition on date X, somewhere else close there is another competition planned on date X which is far more attractive to go to (ex: prize money). Bad luck for your competition then I guess.
I don't think attractiveness would have anything to do with it. If it saves the competitor travel time, they might just go to the close one. "Bad luck"? I thought having well-organized was suppose to be enough?
If you however would increase the number of minimum competitors there would be less competitions and the competition itself would be bigger and attract more (top) cubers, so people would be more likely to all go there. After all: a lot of cubers only attract more cubers...
So less competitions is better? Also, smaller competitions are nice for people who aren't super-elite. At many larger competitions, you have to restrict the number of competitors, many people may not make it beyond qualifying, and therefore may not go.