I recall reading somewhere that only about 10,000 Egyptian Mau kittens were registered by TICA in a recent year for the USA. Only 10,000 kittens! Now not all are registered of course, but let's imagine there were, say, 50,000 Egyptian Mau kittens. If they were sold as pets, they were probably fixed and can't breed. 50,000 kittens x a 20 year life span is 1 million cats. So, the population of Maus is certainly under 1 million in the US and is going to stay low in the foreseeable future.
The breed was only revived from extinction in the 50s, so a lack of time and the control of the breeders keeps the population down. That's really the crux of it. It's the same breeders at all the shows, and very few people can get Maus as pets, because there just isn't enough of them.
And because there aren't many, they are expensive, and so they continue to be rare. It'll take time for this to change.
I think it's a darn shame, because I believe Egyptian Maus are absolutely the best cat, hands-down, in the world. Smart, beautiful, talkative, playful, athletic, magical. But you can only produce so many cats every generation, so I think they will be rare for quite awhile.